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\input texinfo
@c %**start of header
@setfilename dynare.info
@documentencoding UTF-8
@settitle Dynare Reference Manual
@afourwide
@dircategory Math
@direntry
* Dynare: (dynare).             A platform for handling a wide class
                                  of economic models.
@end direntry

@include version.texi

@c Define some macros

@macro descriptionhead
@ifnothtml
@sp 1
@end ifnothtml
@emph{Description}
@end macro

@macro optionshead
@iftex
@sp 1
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@emph{Options}
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@macro flagshead
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@macro examplehead
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@emph{Example}
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@macro outputhead
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@emph{Output}
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@macro customhead{title}
@iftex
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@c %**end of header

@copying
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Copyright @copyright{} 1996-2012, Dynare Team.
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@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.

A copy of the license can be found at @uref{http://www.gnu.org/licenses/fdl.txt}.
@end quotation
@end copying

@titlepage
@title Dynare
@subtitle Reference Manual, version @value{VERSION}
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@author Stéphane Adjemian
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@author Houtan Bastani
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@author Frédéric Karamé
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@author Michel Juillard
@author Junior Maih
@author Ferhat Mihoubi
@author George Perendia
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@author Johannes Pfeifer
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@author Marco Ratto
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@author Sébastien Villemot
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@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top Dynare
This is Dynare Reference Manual, version @value{VERSION}.

@insertcopying
@end ifnottex

@menu
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* Introduction::                
* Installation and configuration::  
* Dynare invocation::           
* The Model file::              
* The Configuration File::      
* Examples::                    
* Dynare internal documentation and unitary tests::  
* Bibliography::                
* Command and Function Index::  
* Variable Index::              
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@detailmenu
 --- The Detailed Node Listing ---

Introduction

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* What is Dynare ?::            
* Documentation sources::       
* Citing Dynare in your research::  
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Installation and configuration

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* Software requirements::       
* Installation of Dynare::      
* Configuration::               
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Installation of Dynare

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* On Windows::                  
* On Debian GNU/Linux and Ubuntu::  
* On Mac OS X::                 
* For other systems::           
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Configuration

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* For MATLAB::                  
* For GNU Octave::              
* Some words of warning::       
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The Model file

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* Conventions::                 
* Variable declarations::       
* Expressions::                 
* Parameter initialization::    
* Model declaration::           
* Auxiliary variables::         
* Initial and terminal conditions::  
* Shocks on exogenous variables::  
* Other general declarations::  
* Steady state::                
* Getting information about the model::  
* Deterministic simulation::    
* Stochastic solution and simulation::  
* Estimation::                  
* Forecasting::                 
* Optimal policy::              
* Sensitivity and identification analysis::  
* Markov-switching SBVAR::      
* Displaying and saving results::  
* Macro-processing language::   
* Misc commands::               
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Expressions

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* Parameters and variables::    
* Operators::                   
* Functions::                   
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Parameters and variables

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* Inside the model::            
* Outside the model::           
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Functions

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* Built-in Functions::          
* External Functions::          
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Steady state

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* Finding the steady state with Dynare nonlinear solver::  
* Using a steady state file::   
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Stochastic solution and simulation

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* Computing the stochastic solution::  
* Typology and ordering of variables::  
* First order approximation::   
* Second order approximation::  
* Third order approximation::   
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Sensitivity and identification analysis

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* Sampling::                    
* Stability Mapping::           
* Reduced Form Mapping::        
* RMSE::                        
* Screening Analysis::          
* Identification Analysis::     
* Performing Sensitivity and Identification Analysis::  
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Macro-processing language

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* Macro expressions::           
* Macro directives::            
* Typical usages::              
* MATLAB/Octave loops versus macro-processor loops::  
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Typical usages

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* Modularization::              
* Indexed sums or products::    
* Multi-country models::        
* Endogeneizing parameters::    
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The Configuration File

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* Dynare Configuration::        
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* Parallel Configuration::      
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@end detailmenu
@end menu

@node Introduction
@chapter Introduction

@menu
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* What is Dynare ?::            
* Documentation sources::       
* Citing Dynare in your research::  
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@end menu

@node What is Dynare ?
@section What is Dynare ?

Dynare is a software platform for handling a wide class of economic
models, in particular dynamic stochastic general equilibrium (DSGE)
and overlapping generations (OLG) models. The models solved by Dynare
include those relying on the @i{rational expectations} hypothesis, wherein
agents form their expectations about the future in a way consistent
with the model. But Dynare is also able to handle models where
expectations are formed differently: on one extreme, models where
agents perfectly anticipate the future; on the other extreme, models
where agents have limited rationality or imperfect knowledge of the
state of the economy and, hence, form their expectations through a
learning process. In terms of types of agents, models solved by Dynare
can incorporate consumers, productive firms, governments, monetary
authorities, investors and financial intermediaries. Some degree of
heterogeneity can be achieved by including several distinct classes of
agents in each of the aforementioned agent categories.

Dynare offers a user-friendly and intuitive way of describing these
models. It is able to perform simulations of the model given a
calibration of the model parameters and is also able to estimate these
parameters given a dataset. In practice, the user will write a text
file containing the list of model variables, the dynamic equations
linking these variables together, the computing tasks to be performed
and the desired graphical or numerical outputs.

A large panel of applied mathematics and computer science techniques
are internally employed by Dynare: multivariate nonlinear solving and
optimization, matrix factorizations, local functional approximation,
Kalman filters and smoothers, MCMC techniques for Bayesian estimation,
graph algorithms, optimal control, @dots{}

Various public bodies (central banks, ministries of economy and
finance, international organisations) and some private financial
institutions use Dynare for performing policy analysis exercises and
as a support tool for forecasting exercises. In the academic world,
Dynare is used for research and teaching purposes in postgraduate
macroeconomics courses.

Dynare is a free software, which means that it can be downloaded free
of charge, that its source code is freely available, and that it can
be used for both non-profit and for-profit purposes. Most of the
source files are covered by the GNU General Public Licence (GPL)
version 3 or later (there are some exceptions to this, see the file
@file{license.txt} in Dynare distribution). It is available for the
Windows, Mac and Linux platforms and is fully documented through a
user guide and a reference manual. Part of Dynare is programmed in
C++, while the rest is written using the
@uref{http://www.mathworks.com/products/matlab/, MATLAB} programming
language.  The latter implies that commercially-available MATLAB
software is required in order to run Dynare. However, as an
alternative to MATLAB, Dynare is also able to run on top of
@uref{http://www.octave.org, GNU Octave} (basically a free clone of
MATLAB): this possibility is particularly interesting for students or
institutions who cannot afford, or do not want to pay for, MATLAB and
are willing to bear the concomitant performance loss.

The development of Dynare is mainly done at
@uref{http://www.cepremap.ens.fr, Cepremap} by a core team of
researchers who devote part of their time to software
development. Currently the development team of Dynare is composed of
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Stéphane Adjemian (Université du Maine, Gains and Cepremap), Houtan
Bastani (Cepremap), Michel Juillard (Banque de France), Frédéric Karamé
(Université d'Évry, Epee and Cepremap), Junior Maih (Norges Bank),
Ferhat Mihoubi (Université d'Évry, Epee and Cepremap), George Perendia,
Johannes Pfeifer, Marco Ratto (JRC) and Sébastien Villemot (Cepremap and
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Paris School of Economics). Increasingly, the developer base is
expanding, as tools developed by researchers outside of Cepremap are
integrated into Dynare. Financial support is provided by Cepremap,
Banque de France and DSGE-net (an international research network for
DSGE modeling). The Dynare project also received funding through the
Seventh Framework Programme for Research (FP7) of the European
Commission's Socio-economic Sciences and Humanities (SSH) Program from
October 2008 to September 2011 under grant agreement SSH-CT-2009-225149.
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Interaction between developers and users of Dynare is central to the
project. A @uref{http://www.dynare.org/phpBB3, web forum} is available
for users who have questions about the usage of Dynare or who want to
report bugs. Training sessions are given through the Dynare Summer
School, which is organized every year and is attended by about 40
people. Finally, priorities in terms of future developments and
features to be added are decided in cooperation with the institutions
providing financial support.

@node Documentation sources
@section Documentation sources

The present document is the reference manual for Dynare. It documents
all commands and features in a systematic fashion.

New users should rather begin with Dynare User Guide (@cite{Mancini
(2007)}), distributed with Dynare and also available from the
@uref{http://www.dynare.org,official Dynare web site}.

Other useful sources of information include the
@uref{http://www.dynare.org,Dynare wiki} and the
@uref{http://www.dynare.org/phpBB3, Dynare forums}.

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@node Citing Dynare in your research
@section Citing Dynare in your research

If you would like to refer to Dynare in a research article, the
recommended way is to cite the present manual, as follows:

@quotation
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Stéphane Adjemian, Houtan Bastani, Michel Juillard, Ferhat Mihoubi,
George Perendia, Marco Ratto and Sébastien Villemot (2011), ``Dynare:
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Reference Manual, Version 4,'' @i{Dynare Working Papers}, 1, CEPREMAP
@end quotation

Note that citing the Dynare Reference Manual in your research is a
good way to help the Dynare project.

If you want to give a URL, use the address of the Dynare website:
@uref{http://www.dynare.org}.

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@node Installation and configuration
@chapter Installation and configuration

@menu
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* Software requirements::       
* Installation of Dynare::      
* Configuration::               
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@end menu

@node Software requirements
@section Software requirements

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Packaged versions of Dynare are available for Windows XP/Vista/Seven,
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@uref{http://www.debian.org,Debian GNU/Linux},
@uref{http://www.ubuntu.com/,Ubuntu} and Mac OS X Leopard/Snow
Leopard.  Dynare should work on other systems, but some compilation
steps are necessary in that case.

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In order to run Dynare, you need one of the following:
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@itemize
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@item
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MATLAB version 7.3 (R2006b) or above;
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@item
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GNU Octave version 3.4.0 or above.
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@end itemize

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Packages of GNU Octave can be downloaded on the
@uref{http://www.dynare.org/download/octave,Dynare website}.
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The following optional extensions are also useful to benefit from extra
features, but are in no way required:

@itemize

@item
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If under MATLAB: the optimization toolbox, the statistics toolbox, the
control system toolbox;
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@item
If under GNU Octave, the following
@uref{http://octave.sourceforge.net/,Octave-Forge} packages: optim,
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io, java, statistics, control.
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@end itemize

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If you plan to use the @code{use_dll} option of the @code{model}
command, you will need to install the necessary requirements for
compiling MEX files on your machine. If you are using MATLAB under
Windows, install a C++ compiler on your machine and configure it with
MATLAB: see
@uref{http://www.dynare.org/DynareWiki/ConfigureMatlabWindowsForMexCompilation,instructions
on the Dynare wiki}. Users of Octave under Linux should install the
package for MEX file compilation (under Debian or Ubuntu, it is called
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@file{liboctave-dev}). If you are
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using Octave or MATLAB under Mac OS X, you should install the latest
version of XCode: see
@uref{http://www.dynare.org/DynareWiki/InstallOnMacOSX,instructions on
the Dynare wiki}. Mac OS X Octave users will also need to install
gnuplot if they want graphing capabilities. Users of MATLAB under
Linux and Mac OS X, and users of Octave under Windows, normally need
to do nothing, since a working compilation environment is available by
default.

@node Installation of Dynare
@section Installation of Dynare

After installation, Dynare can be used in any directory on your
computer. It is best practice to keep your model files in directories
different from the one containing the Dynare toolbox. That way you can
upgrade Dynare and discard the previous version without having to worry
about your own files.

@menu
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* On Windows::                  
* On Debian GNU/Linux and Ubuntu::  
* On Mac OS X::                 
* For other systems::           
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@end menu

@node On Windows
@subsection On Windows

Execute the automated installer called @file{dynare-4.@var{x}.@var{y}-win.exe}
(where 4.@var{x}.@var{y} is the version number), and follow the instructions. The
default installation directory is @file{c:\dynare\4.@var{x}.@var{y}}.

After installation, this directory will contain several sub-directories,
among which are @file{matlab}, @file{mex} and @file{doc}.

The installer will also add an entry in your Start Menu with a shortcut
to the documentation files and uninstaller.

Note that you can have several versions of Dynare coexisting (for
example in @file{c:\dynare}), as long as you correctly adjust your path
settings (@pxref{Some words of warning}).

@node On Debian GNU/Linux and Ubuntu
@subsection On Debian GNU/Linux and Ubuntu

Please refer to the
@uref{http://www.dynare.org/DynareWiki/InstallOnDebianOrUbuntu,Dynare
Wiki} for detailed instructions.

Dynare will be installed under @file{/usr/share/dynare} and
@file{/usr/lib/dynare}. Documentation will be under
@file{/usr/share/doc/dynare}.

@node On Mac OS X
@subsection On Mac OS X

Execute the automated installer called
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@file{dynare-4.@var{x}.@var{y}.pkg} (where
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4.@var{x}.@var{y} is the version number), and follow the
instructions. The default installation directory is
@file{/Applications/Dynare/4.@var{x}.@var{y}}.

Please refer to the
@uref{http://www.dynare.org/DynareWiki/InstallOnMacOSX,Dynare Wiki} for
detailed instructions.

After installation, this directory will contain several sub-directories,
among which are @file{matlab}, @file{mex} and @file{doc}.

Note that you can have several versions of Dynare coexisting (for
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example in @file{/Applications/Dynare}), as long as you correctly
adjust your path settings (@pxref{Some words of warning}).
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@node For other systems
@subsection For other systems

You need to download Dynare source code from the
@uref{http://www.dynare.org,Dynare website} and unpack it somewhere.

Then you will need to recompile the pre-processor and the dynamic
loadable libraries. Please refer to
@uref{http://www.dynare.org/DynareWiki/BuildingDynareFromSource,Dynare
Wiki}.

@node Configuration
@section Configuration

@menu
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* For MATLAB::                  
* For GNU Octave::              
* Some words of warning::       
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@end menu

@node For MATLAB
@subsection For MATLAB

You need to add the @file{matlab} subdirectory of your Dynare
installation to MATLAB path. You have two options for doing that:

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@item
Using the @code{addpath} command in the MATLAB command window:

Under Windows, assuming that you have installed Dynare in the standard
location, and replacing @code{4.@var{x}.@var{y}} with the correct
version number, type:

@example
addpath c:\dynare\4.@var{x}.@var{y}\matlab
@end example

Under Debian GNU/Linux or Ubuntu, type:

@example
addpath /usr/share/dynare/matlab
@end example

Under Mac OS X, assuming that you have installed Dynare in the standard
location, and replacing @code{4.@var{x}.@var{y}} with the correct version
number, type:

@example
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addpath /Applications/Dynare/4.@var{x}.@var{y}/matlab
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@end example

MATLAB will not remember this setting next time you run it, and you
will have to do it again.

@item
Via the menu entries:

Select the ``Set Path'' entry in the ``File'' menu, then click on
``Add Folder@dots{}'', and select the @file{matlab} subdirectory of your
Dynare installation. Note that you @emph{should not} use ``Add with
Subfolders@dots{}''. Apply the settings by clicking on ``Save''. Note that
MATLAB will remember this setting next time you run it.
@end itemize

@node For GNU Octave
@subsection For GNU Octave

You need to add the @file{matlab} subdirectory of your Dynare
installation to Octave path, using the @code{addpath} at the Octave
command prompt.

Under Windows, assuming that you have installed Dynare in the standard
location, and replacing ``4.@var{x}.@var{y}'' with the correct version
number, type:

@example
addpath c:\dynare\4.@var{x}.@var{y}\matlab
@end example

Under Debian GNU/Linux or Ubuntu, there is no need to use the
@code{addpath} command; the packaging does it for you.

Under Mac OS X, assuming that you have installed Dynare in the
standard location, and replacing ``4.@var{x}.@var{y}'' with the correct
version number, type:

@example
addpath /Applications/Dynare/4.@var{x}.@var{y}/matlab
@end example

If you don't want to type this command every time you run Octave, you
can put it in a file called @file{.octaverc} in your home directory
(under Windows this will generally by @file{c:\Documents and
Settings\USERNAME\}). This file is run by Octave at every startup.

@node Some words of warning
@subsection Some words of warning

You should be very careful about the content of your MATLAB or Octave
path. You can display its content by simply typing @code{path} in the
command window.

The path should normally contain system directories of MATLAB or Octave,
and some subdirectories of your Dynare installation. You have to
manually add the @file{matlab} subdirectory, and Dynare will
automatically add a few other subdirectories at runtime (depending on
your configuration). You must verify that there is no directory coming
from another version of Dynare than the one you are planning to use.

You have to be aware that adding other directories to your path can
potentially create problems, if some of your M-files have the same names
than Dynare files. Your files would then override Dynare files, and make
Dynare unusable.

@node Dynare invocation
@chapter Dynare invocation

In order to give instructions to Dynare, the user has to write a
@emph{model file} whose filename extension must be @file{.mod}. This
file contains the description of the model and the computing tasks
required by the user. Its contents is described in @ref{The Model file}.

Once the model file is written, Dynare is invoked using the
@code{dynare} command at the MATLAB or Octave prompt (with the filename
of the @file{.mod} given as argument).

In practice, the handling of the model file is done in two steps: in the
first one, the model and the processing instructions written by the user
in a @emph{model file} are interpreted and the proper MATLAB or GNU
Octave instructions are generated; in the second step, the program
actually runs the computations. Boths steps are triggered automatically
by the @code{dynare} command.

@deffn {MATLAB/Octave command} dynare @var{FILENAME}[.mod] [@var{OPTIONS}@dots{}]

@descriptionhead

This command launches Dynare and executes the instructions included in
@file{@var{FILENAME}.mod}.  This user-supplied file contains the model
and the processing instructions, as described in @ref{The Model file}.

@code{dynare} begins by launching the preprocessor on the @file{.mod}
file.  By default (unless @code{use_dll} option has been given to
@code{model}), the preprocessor creates three intermediary files:

@table @file

@item @var{FILENAME}.m
Contains variable declarations, and computing tasks

@item @var{FILENAME}_dynamic.m
Contains the dynamic model equations

@item @var{FILENAME}_static.m
Contains the long run static model equations
@end table

@noindent
These files may be looked at to understand errors reported at the simulation stage.

@code{dynare} will then run the computing tasks by executing @file{@var{FILENAME}.m}.

@optionshead

@table @code

@item noclearall
By default, @code{dynare} will issue a @code{clear all} command to
MATLAB or Octave, thereby deleting all workspace variables; this options
instructs @code{dynare} not to clear the workspace

@item debug
Instructs the preprocessor to write some debugging information about the
scanning and parsing of the @file{.mod} file

@item notmpterms
Instructs the preprocessor to omit temporary terms in the static and
dynamic files; this generally decreases performance, but is used for
debugging purposes since it makes the static and dynamic files more
readable

@item savemacro[=@var{FILENAME}]
Instructs @code{dynare} to save the intermediary file which is obtained
after macro-processing (@pxref{Macro-processing language}); the saved
output will go in the file specified, or if no file is specified in
@file{@var{FILENAME}-macroexp.mod}

@item onlymacro
Instructs the preprocessor to only perform the macro-processing step,
and stop just after. Mainly useful for debugging purposes or for using
the macro-processor independently of the rest of Dynare toolbox.

@item nolinemacro
Instructs the macro-preprocessor to omit line numbering information in
the intermediary @file{.mod} file created after the maco-processing
step. Useful in conjunction with @code{savemacro} when one wants that to
reuse the intermediary @file{.mod} file, without having it cluttered by
line numbering directives.

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@item nolog
Instructs Dynare to no create a logfile of this run in
@file{@var{FILENAME}.log}. The default is to create the logfile.

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@item warn_uninit
Display a warning for each variable or parameter which is not
initialized. @xref{Parameter initialization}, or
@ref{load_params_and_steady_state} for initialization of parameters.
@xref{Initial and terminal conditions}, or
@ref{load_params_and_steady_state} for initialization of endogenous
and exogenous variables.

@item console
Activate console mode: Dynare will not use graphical waitbars for long
computations. Note that this option is only useful under MATLAB, since
Octave does not provide graphical waitbar capabilities.

@item cygwin
Tells Dynare that your MATLAB is configured for compiling MEX files with
Cygwin (@pxref{Software requirements}). This option is only available
under Windows, and is used in conjunction with @code{use_dll}.

@item msvc
Tells Dynare that your MATLAB is configured for compiling MEX files with
Microsoft Visual C++ (@pxref{Software requirements}). This option is
only available under Windows, and is used in conjunction with
@code{use_dll}.

@item parallel[=@var{CLUSTER_NAME}]
Tells Dynare to perform computations in parallel. If @var{CLUSTER_NAME}
is passed, Dynare will use the specified cluster to perform parallel
computations. Otherwise, Dynare will use the first cluster specified in
the configuration file. @xref{The Configuration File}, for more
information about the configuration file.

@item conffile=@var{FILENAME}
Specifies the location of the configuration file if it differs from the
default. @xref{The Configuration File}, for more information about the
configuration file and its default location.

@item parallel_slave_open_mode
Instructs Dynare to leave the connection to the slave node open after
computation is complete, closing this connection only when Dynare
finishes processing.

@item parallel_test
Tests the parallel setup specified in the configuration file without
executing the @file{.mod} file. @xref{The Configuration File}, for more
information about the configuration file.
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@item -D@var{MACRO_VARIABLE}=@var{MACRO_EXPRESSION}
Defines a macro-variable from the command line (the same effect as using
the Macro directive @code{@@#define} in a model file, @pxref{Macro-processing language}).
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@end table

@outputhead

Depending on the computing tasks requested in the @file{.mod} file,
executing command @code{dynare} will leave in the workspace variables
containing results available for further processing. More details are
given under the relevant computing tasks.

The @code{M_}, @code{oo_} and @code{options_} structures are also saved
in a file called @file{@var{FILENAME}_results.mat}.

@examplehead

@example
dynare ramst
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dynare ramst.mod savemacro
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@end example

@end deffn

The output of Dynare is left into three main variables in the
MATLAB/Octave workspace:

@defvr {MATLAB/Octave variable} M_
Structure containing various informations about the model.
@end defvr

@defvr {MATLAB/Octave variable} options_
Structure contains the values of the various options used by Dynare
during the computation.
@end defvr

@defvr {MATLAB/Octave variable} oo_
Structure containing the various results of the computations.
@end defvr

@node The Model file
@chapter The Model file

@menu
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* Conventions::                 
* Variable declarations::       
* Expressions::                 
* Parameter initialization::    
* Model declaration::           
* Auxiliary variables::         
* Initial and terminal conditions::  
* Shocks on exogenous variables::  
* Other general declarations::  
* Steady state::                
* Getting information about the model::  
* Deterministic simulation::    
* Stochastic solution and simulation::  
* Estimation::                  
* Forecasting::                 
* Optimal policy::              
* Sensitivity and identification analysis::  
* Markov-switching SBVAR::      
* Displaying and saving results::  
* Macro-processing language::   
* Misc commands::               
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@end menu

@node Conventions
@section Conventions

A model file contains a list of commands and of blocks.  Each command
and each element of a block is terminated by a semicolon
(@code{;}). Blocks are terminated by @code{end;}.

Most Dynare commands have arguments and several accept options,
indicated in parentheses after the command keyword. Several options
are separated by commas.

In the description of Dynare commands, the following conventions are
observed:

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@itemize
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@item
optional arguments or options are indicated between square brackets:
@samp{[]};

@item
repreated arguments are indicated by ellipses: ``@dots{}'';

@item
mutually exclusive arguments are separated by vertical bars: @samp{|};

@item
@var{INTEGER} indicates an integer number;

@item
@var{DOUBLE} indicates a double precision number. The following syntaxes
are valid: @code{1.1e3}, @code{1.1E3}, @code{1.1d3}, @code{1.1D3};

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@item
@var{NUMERICAL_VECTOR} indicates a vector of numbers separated by spaces,
enclosed by square brackets;

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@item
@var{EXPRESSION} indicates a mathematical expression valid outside the
model description (@pxref{Expressions});

@item
@var{MODEL_EXPRESSION} indicates a mathematical expression valid in the
model description (@pxref{Expressions} and @ref{Model declaration});

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@item
@var{MACRO_EXPRESSION} designates an expression of the macro-processor
(@pxref{Macro expressions});

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@item
@var{VARIABLE_NAME} indicates a variable name starting with an
alphabetical character and can't contain: @samp{()+-*/^=!;:@@#.} or
accentuated characters;

@item
@var{PARAMETER_NAME} indicates a parameter name starting with an
alphabetical character and can't contain: @samp{()+-*/^=!;:@@#.} or
accentuated characters;

@item
@var{LATEX_NAME} indicates a valid LaTeX expression in math mode (not
including the dollar signs);

@item
@var{FUNCTION_NAME} indicates a valid MATLAB function name;

@item
@var{FILENAME} indicates a filename valid in the underlying operating
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system; it is necessary to put it between quotes when specifying the
extension or if the filename contains a non-alphanumeric character;
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@end itemize

@node Variable declarations
@section Variable declarations

Declarations of variables and parameters are made with the following commands:

@deffn Command var @var{VARIABLE_NAME} [$@var{LATEX_NAME}$]@dots{};
@deffnx Command var (deflator = @var{MODEL_EXPRESSION}) @var{VARIABLE_NAME} [$@var{LATEX_NAME}$]@dots{};

@descriptionhead

This required command declares the endogenous variables in the
model. @xref{Conventions}, for the syntax of @var{VARIABLE_NAME} and
@var{MODEL_EXPRESSION}. Optionally it is possible to give a LaTeX name
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to the variable or, if it is nonstationary, provide information regarding
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its deflator.

@code{var} commands can appear several times in the file and Dynare will
concatenate them.

@optionshead

If the model is nonstationary and is to be written as such in the
@code{model} block, Dynare will need the trend deflator for the
appropriate endogenous variables in order to stationarize the model. The
trend deflator must be provided alongside the variables that follow this
trend.

@table @code

@item deflator = @var{MODEL_EXPRESSION}
The expression used to detrend an endogenous variable. All trend
variables, endogenous variables and parameters referenced in
@var{MODEL_EXPRESSION} must already have been declared by the
@code{trend_var}, @code{var} and @code{parameters} commands.
@end table

@examplehead

@example
var c gnp q1 q2;
var(deflator=A) i b;
@end example

@end deffn

@deffn Command varexo @var{VARIABLE_NAME} [$@var{LATEX_NAME}$]@dots{};

@descriptionhead

This optional command declares the exogenous variables in the model.
@xref{Conventions}, for the syntax of @var{VARIABLE_NAME}. Optionally it
is possible to give a LaTeX name to the variable.

Exogenous variables are required if the user wants to be able to apply
shocks to her model.

@code{varexo} commands can appear several times in the file and Dynare
will concatenate them.

@examplehead

@example
varexo m gov;
@end example

@end deffn

@deffn Command varexo_det @var{VARIABLE_NAME} [$@var{LATEX_NAME}$]@dots{};

@descriptionhead

This optional command declares exogenous deterministic variables in a
stochastic model. See @ref{Conventions}, for the syntax of
@var{VARIABLE_NAME}. Optionally it is possible to give a LaTeX name to
the variable.

It is possible to mix deterministic and stochastic shocks to build
models where agents know from the start of the simulation about future
exogenous changes. In that case @code{stoch_simul} will compute the
rational expectation solution adding future information to the state
space (nothing is shown in the output of @code{stoch_simul}) and
@code{forecast} will compute a simulation conditional on initial
conditions and future information.

@code{varexo_det} commands can appear several times in the file and
Dynare will concatenate them.

@examplehead

@example

varexo m gov;
varexo_det tau;
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@end example

@end deffn

@deffn Command parameters @var{PARAMETER_NAME} [$@var{LATEX_NAME}$]@dots{};

@descriptionhead

This command declares parameters used in the model, in variable
initialization or in shocks declarations. See @ref{Conventions}, for the
syntax of @var{PARAMETER_NAME}. Optionally it is possible to give a
LaTeX name to the parameter.

The parameters must subsequently be assigned values (@pxref{Parameter
initialization}).

@code{parameters} commands can appear several times in the file and
Dynare will concatenate them.

@examplehead

@example
parameters alpha, bet;
@end example

@end deffn

@deffn Command change_type (var | varexo | varexo_det | parameters) @var{VARIABLE_NAME} | @var{PARAMETER_NAME}@dots{};

@descriptionhead

Changes the types of the specified variables/parameters to another type:
endogenous, exogenous, exogenous deterministic or parameter.

It is important to understand that this command has a global effect on
the @file{.mod} file: the type change is effective after, but also
before, the @code{change_type} command. This command is typically used
when flipping some variables for steady state calibration: typically a
separate model file is used for calibration, which includes the list of
variable declarations with the macro-processor, and flips some variable.

@examplehead

@example
var y, w;
parameters alpha, bet;
@dots{}
change_type(var) alpha, bet;
change_type(parameters) y, w;
@end example

Here, in the whole model file, @code{alpha} and @code{beta} will be
endogenous and @code{y} and @code{w} will be parameters.

@end deffn

@anchor{predetermined_variables}
@deffn Command predetermined_variables @var{VARIABLE_NAME}@dots{};

@descriptionhead

In Dynare, the default convention is that the timing of a variable
reflects when this variable is decided. The typical example is for
capital stock: since the capital stock used at current period is
actually decided at the previous period, then the capital stock entering
the production function is @code{k(-1)}, and the law of motion of
capital must be written:

@example
k = i + (1-delta)*k(-1)
@end example

Put another way, for stock variables, the default in Dynare is to use a
``stock at the end of the period'' concept, instead of a ``stock at the
beginning of the period'' convention.

The @code{predetermined_variables} is used to change that
convention. The endogenous variables declared as predetermined variables
are supposed to be decided one period ahead of all other endogenous
variables. For stock variables, they are supposed to follow a ``stock at
the beginning of the period'' convention.

@examplehead

The following two program snippets are strictly equivalent.

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@emph{Using default Dynare timing convention:}
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@example
var y, k, i;
@dots{}
model;
y = k(-1)^alpha;
k = i + (1-delta)*k(-1);
@dots{}
end;
@end example

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@emph{Using the alternative timing convention:}
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@example
var y, k, i;
predetermined_variables k;
@dots{}
model;
y = k^alpha;
k(+1) = i + (1-delta)*k;
@dots{}
end;
@end example

@end deffn

@deffn Command trend_var (growth_factor = @var{MODEL_EXPRESSION}) @var{VARIABLE_NAME} [$@var{LATEX_NAME}$]@dots{};

@descriptionhead

This optional command declares the trend variables in the
model. @xref{Conventions}, for the syntax of @var{MODEL_EXPRESSION} and
@var{VARIABLE_NAME}. Optionally it is possible to give a LaTeX name to
the variable.

Trend variables are required if the user wants to be able to write a
nonstationary model in the @code{model} block. The @code{trend_var}
command must appear before the @code{var} command that references the
trend variable.

@code{trend_var} commands can appear several times in the file and
Dynare will concatenate them.

If the model is nonstationary and is to be written as such in the
@code{model} block, Dynare will need the growth factor of every trend
variable in order to stationarize the model. The growth factor must be
provided within the declaration of the trend variable, using the
@code{growth_factor} keyword. All endogenous variables and
parameters referenced in @var{MODEL_EXPRESSION} must already have been
declared by the @code{var} and @code{parameters} commands.

@examplehead

@example
trend_var (growth_factor=gA) A;
@end example

@end deffn

@node Expressions
@section Expressions

Dynare distinguishes between two types of mathematical expressions:
those that are used to describe the model, and those that are used
outside the model block (@i{e.g.} for initializing parameters or
variables, or as command options). In this manual, those two types of
expressions are respectively denoted by @var{MODEL_EXPRESSION} and
@var{EXPRESSION}.

Unlike MATLAB or Octave expressions, Dynare expressions are necessarily
scalar ones: they cannot contain matrices or evaluate to
matrices@footnote{Note that arbitrary MATLAB or Octave expressions can
be put in a @file{.mod} file, but those expressions have to be on
separate lines, generally at the end of the file for post-processing
purposes. They are not interpreted by Dynare, and are simply passed on
unmodified to MATLAB or Octave. Those constructions are not addresses in
this section.}.

Expressions can be constructed using integers (@var{INTEGER}), floating
point numbers (@var{DOUBLE}), parameter names (@var{PARAMETER_NAME}),
variable names (@var{VARIABLE_NAME}), operators and functions.

The following special constants are also accepted in some contexts:

@deffn Constant inf
Represents infinity.
@end deffn

@deffn Constant nan
``Not a number'': represents an undefined or unrepresentable value.
@end deffn

@menu
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* Parameters and variables::    
* Operators::                   
* Functions::                   
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@end menu

@node Parameters and variables
@subsection Parameters and variables

Parameters and variables can be introduced in expressions by simply
typing their names. The semantics of parameters and variables is quite
different whether they are used inside or outside the model block.

@menu
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* Inside the model::            
* Outside the model::           
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@end menu

@node Inside the model
@subsubsection Inside the model

Parameters used inside the model refer to the value given through
parameter initialization (@pxref{Parameter initialization}) or
@code{homotopy_setup} when doing a simulation, or are the estimated
variables when doing an estimation.

Variables used in a @var{MODEL_EXPRESSION} denote @emph{current period}
values when neither a lead or a lag is given. A lead or a lag can be
given by enclosing an integer between parenthesis just after the
variable name: a positive integer means a lead, a negative one means a
lag. Leads or lags of more than one period are allowed. For example, if
@code{c} is an endogenous variable, then @code{c(+1)} is the variable
one period ahead, and @code{c(-2)} is the variable two periods before.

When specifying the leads and lags of endogenous variables, it is
important to respect the following convention: in Dynare, the timing of
a variable reflects when that variable is decided. A control variable ---
which by definition is decided in the current period --- must have no
lead. A predetermined variable --- which by definition has been decided in
a previous period --- must have a lag. A consequence of this is that all
stock variables must use the ``stock at the end of the period''
convention. Please refer to @cite{Mancini-Griffoli (2007)} for more
details and concrete examples.

Leads and lags are primarily used for endogenous variables, but can be
used for exogenous variables. They have no effect on parameters and are
forbidden for local model variables (@pxref{Model declaration}).

@node Outside the model
@subsubsection Outside the model

When used in an expression outside the model block, a parameter or a
variable simply refers to the last value given to that variable. More
precisely, for a parameter it refers to the value given in the
corresponding parameter initialization (@pxref{Parameter
initialization}); for an endogenous or exogenous variable, it refers to
the value given in the most recent @code{initval} or @code{endval} block.

@node Operators
@subsection Operators

The following operators are allowed in both @var{MODEL_EXPRESSION} and
@var{EXPRESSION}:

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@item
binary arithmetic operators: @code{+}, @code{-}, @code{*}, @code{/}, @code{^}

@item
unary arithmetic operators: @code{+}, @code{-}

@item
binary comparison operators (which evaluate to either @code{0} or
@code{1}): @code{<}, @code{>}, @code{<=}, @code{>=}, @code{==},
@code{!=}
@end itemize

The following special operators are accepted in @var{MODEL_EXPRESSION}
(but not in @var{EXPRESSION}):

@deffn Operator STEADY_STATE (@var{MODEL_EXPRESSION})
This operator is used to take the value of the enclosed expression at
the steady state. A typical usage is in the Taylor rule, where you may
want to use the value of GDP at steady state to compute the output gap.
@end deffn

@anchor{expectation}
@deffn Operator EXPECTATION (@var{INTEGER}) (@var{MODEL_EXPRESSION})
This operator is used to take the expectation of some expression using
a different information set than the information available at current
period. For example, @code{EXPECTATION(-1)(x(+1))} is equal to the
expected value of variable @code{x} at next period, using the
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variables}, for an explanation of how this operator is handled
internally and how this affects the output.
@end deffn

@node Functions
@subsection Functions

@menu
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* Built-in Functions::          
* External Functions::          
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@end menu

@node Built-in Functions
@subsubsection Built-in Functions

The following standard functions are supported internally for both
@var{MODEL_EXPRESSION} and @var{EXPRESSION}:

@defun exp (@var{x})
Natural exponential.
@end defun

@defun log (@var{x})
@defunx ln (@var{x})
Natural logarithm.
@end defun

@defun log10 (@var{x})
Base 10 logarithm.
@end defun

@defun sqrt (@var{x})
Square root.
@end defun

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@defun abs (@var{x})
Absolute value.
@end defun

@defun sign (@var{x})
Signum function.
@end defun

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@defun sin (@var{x})
@defunx cos (@var{x})
@defunx tan (@var{x})
@defunx asin (@var{x})
@defunx acos (@var{x})
@defunx atan (@var{x})
Trigonometric functions.
@end defun

@defun max (@var{a}, @var{b})
@defunx min (@var{a}, @var{b})
Maximum and minimum of two reals.
@end defun

@defun normcdf (@var{x})
@defunx normcdf (@var{x}, @var{mu}, @var{sigma})
Gaussian cumulative density function, with mean @var{mu} and standard
deviation @var{sigma}. Note that @code{normcdf(@var{x})} is equivalent
to @code{normcdf(@var{x},0,1)}.
@end defun

@defun normpdf (@var{x})
@defunx normpdf (@var{x}, @var{mu}, @var{sigma})
Gaussian probability density function, with mean @var{mu} and standard
deviation @var{sigma}. Note that @code{normpdf(@var{x})} is equivalent
to @code{normpdf(@var{x},0,1)}.
@end defun

@defun erf (@var{x})
Gauss error function.
@end defun

@node External Functions
@subsubsection External Functions

Any other user-defined (or built-in) MATLAB or Octave function may be
used in both a @var{MODEL_EXPRESSION} and an @var{EXPRESSION}, provided
that this function has a scalar argument as a return value.

To use an external function in a @var{MODEL_EXPRESSION}, one must
declare the function using the @code{external_function} statement. This
is not necessary for external functions used in an @var{EXPRESSION}.

@deffn Command external_function (@var{OPTIONS}@dots{});

@descriptionhead

This command declares the external functions used in the model block. It
is required for every unique function used in the model block.

@code{external_function} commands can appear several times in the file
and must come before the model block.

@optionshead

@table @code

@item name = @var{NAME}
The name of the function, which must also be the name of the M-/MEX file
implementing it. This option is mandatory.

@item nargs = @var{INTEGER}
The number of arguments of the function. If this option is not provided,
Dynare assumes @code{nargs = 1}.

@item first_deriv_provided [= @var{NAME}]
If @var{NAME} is provided, this tells Dynare that the Jacobian is
provided as the only output of the M-/MEX file given as the option
argument. If @var{NAME} is not provided, this tells Dynare that the
M-/MEX file specified by the argument passed to @code{name} returns the
Jacobian as its second output argument.

@item second_deriv_provided [= @var{NAME}]
If @var{NAME} is provided, this tells Dynare that the Hessian is
provided as the only output of the M-/MEX file given as the option
argument. If @var{NAME} is not provided, this tells Dynare that the
M-/MEX file specified by the argument passed to @code{name} returns the
Hessian as its third output argument. NB: This option can only be used
if the @code{first_deriv_provided} option is used in the same
@code{external_function} command.
@end table

@examplehead

@example
external_function(name = funcname);
external_function(name = otherfuncname, nargs = 2,
                  first_deriv_provided, second_deriv_provided);
external_function(name = yetotherfuncname, nargs = 3,
                  first_deriv_provided = funcname_deriv);
@end example

@end deffn

@node Parameter initialization
@section Parameter initialization

When using Dynare for computing simulations, it is necessary to
calibrate the parameters of the model. This is done through parameter
initialization.

The syntax is the following:

@example
@var{PARAMETER_NAME} = @var{EXPRESSION};
@end example

Here is an example of calibration:

@example
parameters alpha, bet;

beta = 0.99;
alpha = 0.36;
A = 1-alpha*beta;
@end example

Internally, the parameter values are stored in @code{M_.params}:

@defvr {MATLAB/Octave variable} M_.params

Contains the values of model parameters. The parameters are in the
order that was used in the @code{parameters} command.

@end defvr


@node Model declaration
@section Model declaration

The model is declared inside a @code{model} block:

@deffn Block model ;
@deffnx Block model (@var{OPTIONS}@dots{});

@descriptionhead

The equations of the model are written in a block delimited by
@code{model} and @code{end} keywords.

There must be as many equations as there are endogenous variables in the
model, except when computing the unconstrained optimal policy with
@code{ramsey_policy} or @code{discretionary_policy}.

The syntax of equations must follow the conventions for
@var{MODEL_EXPRESSION} as described in @ref{Expressions}. Each equation
must be terminated by a semicolon (@samp{;}). A normal equation looks
like:
@example
@var{MODEL_EXPRESSION} = @var{MODEL_EXPRESSION};
@end example

When the equations are written in homogenous form, it is possible to
omit the @samp{=0} part and write only the left hand side of the
equation. A homogenous equation looks like:
@example
@var{MODEL_EXPRESSION};
@end example

Inside the model block, Dynare allows the creation of @emph{model-local
variables}, which constitute a simple way to share a common expression
between several equations. The syntax consists of a pound sign
(@code{#}) followed by the name of the new model local variable (which
must @strong{not} be declared as in @ref{Variable declarations}), an equal
sign, and the expression for which this new variable will stand. Later
on, every time this variable appears in the model, Dynare will
substitute it by the expression assigned to the variable. Note that the
scope of this variable is restricted to the model block; it cannot be
used outside. A model local variable declaration looks like:
@example
# @var{VARIABLE_NAME} = @var{MODEL_EXPRESSION};
@end example

@optionshead

@table @code

@item linear
Declares the model as being linear. It spares oneself from having to
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declare initial values for computing the steady state of a stationary
linear model. This options can't be used with non-linear models, it will
NOT trigger linearization of the model.
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@item use_dll
@anchor{use_dll}
Instructs the preprocessor to create dynamic loadable libraries (DLL)
containing the model equations and derivatives, instead of writing those
in M-files. You need a working compilation environment, @i{i.e.}
a working @code{mex} command (see @ref{Software requirements} for more
details). Using this option can result in faster simulations or
estimations, at the expense of some initial compilation
time.@footnote{In particular, for big models, the compilation step can
be very time-consuming, and use of this option may be counter-productive
in those cases.}

@item block
@anchor{block}
Perform the block decomposition of the model, and exploit it in
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computations (steady-state, deterministic simulation, 
stochastic simulation with first order approximation and estimation). See
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@uref{http://www.dynare.org/DynareWiki/FastDeterministicSimulationAndSteadyStateComputation,Dynare
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wiki} for details on the algorithms used in deterministic simulation and steady-state computation.
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@item bytecode
@anchor{bytecode}
Instead of M-files, use a bytecode representation of the model, @i{i.e.}
a binary file containing a compact representation of all the equations.

@item cutoff = @var{DOUBLE}
Threshold under which a jacobian element is considered as null during
the model normalization. Only available with option
@code{block}. Default: @code{1e-15}

@item mfs = @var{INTEGER}
Controls the handling of minimum feedback set of endogenous
variables. Only available with option @code{block}. Possible values:

@table @code

@item 0
All the endogenous variables are considered as feedback variables (Default).

@item 1
The endogenous variables assigned to equation naturally normalized
(@i{i.e.} of the form @math{x=f(Y)} where @math{x} does not appear in
@math{Y}) are potentially recursive variables. All the other variables
are forced to belong to the set of feedback variables.

@item 2
In addition of variables with @code{mfs = 1} the endogenous variables
related to linear equations which could be normalized are potential
recursive variables. All the other variables are forced to belong to
the set of feedback variables.

@item 3
In addition of variables with @code{mfs = 2} the endogenous variables
related to non-linear equations which could be normalized are
potential recursive variables. All the other variables are forced to
belong to the set of feedback variables.
@end table

@item no_static
Don't create the static model file. This can be useful for models which
don't have a steady state.
@end table

@customhead{Example 1: elementary RBC model}

@example
var c k;
varexo x;
parameters aa alph bet delt gam;

model;
c =  - k + aa*x*k(-1)^alph + (1-delt)*k(-1);
c^(-gam) = (aa*alph*x(+1)*k^(alph-1) + 1 - delt)*c(+1)^(-gam)/(1+bet);
end;
@end example

@customhead{Example 2: use of model local variables}

The following program:

@example
model;
# gamma = 1 - 1/sigma;
u1 = c1^gamma/gamma;
u2 = c2^gamma/gamma;
end;
@end example

@noindent
@dots{}is formally equivalent to:

@example
model;
u1 = c1^(1-1/sigma)/(1-1/sigma);
u2 = c2^(1-1/sigma)/(1-1/sigma);
end;
@end example

@customhead{Example 3: a linear model}

@example
model(linear);
x = a*x(-1)+b*y(+1)+e_x;
y = d*y(-1)+e_y;
end;
@end example

@end deffn

Dynare has the ability to output the list of model equations to a
LaTeX file, using the @code{write_latex_dynamic_model} command. The
static model can also be written with the
@code{write_latex_static_model} command.

@anchor{write_latex_dynamic_model}
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@deffn Command write_latex_dynamic_model ;

@descriptionhead

This command creates a LaTeX file containing the (dynamic) model.

If your @file{.mod} file is @file{@var{FILENAME}.mod}, then Dynare
will create a file called @file{@var{FILENAME}_dynamic.tex},
containing the list of all the dynamic model equations.

If LaTeX names were given for variables and parameters
(@pxref{Variable declarations}), then those will be used; otherwise,
the plain text names will be used.

Time subscripts (@code{t}, @code{t+1}, @code{t-1}, @dots{}) will be
appended to the variable names, as LaTeX subscripts.

Note that the model written in the TeX file will differ from the model
declared by the user in the following dimensions:

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@itemize
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@item
the timing convention of predetermined variables
(@pxref{predetermined_variables}) will have been changed to the
default Dynare timing convention; in other words, variables declared
as predetermined will be lagged on period back,

@item
the expectation operators (@pxref{expectation}) will have
been removed, replaced by auxiliary variables and new equations as
explained in the documentation of the operator,

@item
endogenous variables with leads or lags greater or equal than two will
have been removed, replaced by new auxiliary variables and equations,

@item
for a stochastic model, exogenous variables with leads or lags will
also have been replaced by new auxiliary variables and equations.
@end itemize

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Compiling the TeX file requires the following Latex packages: 
@code{geometry}, @code{fullpage}, @code{breqn}.

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@end deffn

@deffn Command write_latex_static_model ;

@descriptionhead

This command creates a LaTeX file containing the static model.

If your @file{.mod} file is @file{@var{FILENAME}.mod}, then Dynare
will create a file called @file{@var{FILENAME}_static.tex}, containing
the list of all the equations of the steady state model.

If LaTeX names were given for variables and parameters
(@pxref{Variable declarations}), then those will be used; otherwise,
the plain text names will be used.

Note that the model written in the TeX file will differ from the model
declared by the user in the some dimensions
(@pxref{write_latex_dynamic_model} for details).

Also note that this command will not output the contents of the
optional @code{steady_state_model} block (@pxref{steady_state_model});
it will rather output a static version (@i{i.e.} without leads and
lags) of the dynamic model declared in the @code{model} block.

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Compiling the TeX file requires the following Latex packages: 
@code{geometry}, @code{fullpage}, @code{breqn}.

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@end deffn

@node Auxiliary variables
@section Auxiliary variables

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The model which is solved internally by Dynare is not exactly the
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model declared by the user. In some cases, Dynare will introduce
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auxiliary endogenous variables---along with corresponding auxiliary
equations---which will appear in the final output.
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The main transformation concerns leads and lags. Dynare will perform a
transformation of the model so that there is only one lead and one lag
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on endogenous variables and, in the case of a stochastic model, no leads/lags on
exogenous variables.
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This transformation is achieved by the creation of auxiliary
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variables and corresponding equations. For example, if @code{x(+2)}
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exists in the model, Dynare will create one auxiliary variable
@code{AUX_ENDO_LEAD = x(+1)}, and replace @code{x(+2)} by
@code{AUX_ENDO_LEAD(+1)}.

A similar transformation is done for lags greater than 2 on endogenous
(auxiliary variables will have a name beginning with
@code{AUX_ENDO_LAG}), and for exogenous with leads and lags (auxiliary
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variables will have a name beginning with @code{AUX_EXO_LEAD} or
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@code{AUX_EXO_LAG} respectively).

Another transformation is done for the @code{EXPECTATION}
operator. For each occurence of this operator, Dynare creates an
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auxiliary variable defined by a new equation, and replaces the
expectation operator by a reference to the new auxiliary variable. For
example, the expression @code{EXPECTATION(-1)(x(+1))} is replaced by
@code{AUX_EXPECT_LAG_1(-1)}, and the new auxiliary variable is
declared as @code{AUX_EXPECT_LAG_1 = x(+2)}.
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Auxiliary variables are also introduced by the preprocessor for the
@code{ramsey_policy} command. In this case, they are used to represent the Lagrange
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multipliers when first order conditions of the Ramsey problem are computed.
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The new variables take the form @code{MULT_@var{i}}, where @var{i} represents
the constraint with which the multiplier is associated (counted from the
order of declaration in the model block).

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Once created, all auxiliary variables are included in the set of
endogenous variables. The output of decision rules (see below) is such
that auxiliary variable names are replaced by the original variables
they refer to.

@vindex M_.orig_endo_nbr
@vindex M_.endo_nbr
The number of endogenous variables before the creation of auxiliary
variables is stored in @code{M_.orig_endo_nbr}, and the number of
endogenous variables after the creation of auxiliary variables is
stored in @code{M_.endo_nbr}.

See @uref{http://www.dynare.org/DynareWiki/AuxiliaryVariables,Dynare
Wiki} for more technical details on auxiliary variables.

@node Initial and terminal conditions
@section Initial and terminal conditions

For most simulation exercises, it is necessary to provide initial (and
possibly terminal) conditions. It is also necessary to provide initial
guess values for non-linear solvers. This section describes the
statements used for those purposes.

In many contexts (determistic or stochastic), it is necessary to
compute the steady state of a non-linear model: @code{initval} then
specifies numerical initial values for the non-linear solver. The
command @code{resid} can be used to compute the equation residuals for
the given initial values.

Used in perfect foresight mode, the types of forward-loking models for
which Dynare was designed require both initial and terminal
conditions. Most often these initial and terminal conditions are
static equilibria, but not necessarily.

One typical application is to consider an economy at the equilibrium,
trigger a shock in first period, and study the trajectory of return at
the initial equilbrium. To do that, one needs @code{initval} and
@code{shocks} (@pxref{Shocks on exogenous variables}.

Another one is to study, how an economy, starting from arbitrary
initial conditions converges toward equilibrium. To do that, one needs
@code{initval} and @code{endval}.

For models with lags on more than one period, the command
@code{histval} permits to specify different historical initial values
for periods before the beginning of the simulation.

@deffn Block initval ;

@descriptionhead

The @code{initval} block serves two purposes: declaring the initial
(and possibly terminal) conditions in a simulation exercise, and
providing guess values for non-linear solvers.

This block is terminated by @code{end;}, and contains lines of the
form:
@example
@var{VARIABLE_NAME} = @var{EXPRESSION};
@end example

@customhead{In a deterministic (@i{i.e.} perfect foresight) model}

First, it provides the initial conditions for all the endogenous and
exogenous variables at all the periods preceeding the first simulation
period (unless some of these initial values are modified by
@code{histval}).

Second, in the absence of an @code{endval} block, it sets the terminal
conditions for all the periods succeeding the last simulation period.

Third, in the absence of an @code{endval} block, it provides initial
guess values at all simulation dates for the non-linear solver
implemented in @code{simul}.

For this last reason, it necessary to provide values for all the
endogenous variables in an @code{initval} block (even though,
theoretically, initial conditions are only necessary for lagged
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@code{initval} block, a zero value is assumed.

Note that if the @code{initval} block is immediately followed by a
@code{steady} command, its semantics is changed. The @code{steady}
command will compute the steady state of the model for all the
endogenous variables, assuming that exogenous variables are kept
constant to the value declared in the @code{initval} block, and using
the values declared for the endogenous as initial guess values for the
non-linear solver. An @code{initval} block followed by @code{steady}
is formally equivalent to an @code{initval} block with the same values
for the exogenous, and with the associated steady state values for the
endogenous.

@customhead{In a stochastic model}

The main purpose of @code{initval} is to provide initial guess values
for the non-linear solver in the steady state computation. Note that
if the @code{initval} block is not followed by @code{steady}, the
steady state computation will still be triggered by subsequent
commands (@code{stoch_simul}, @code{estimation}@dots{}).

It is not necessary to declare @code{0} as initial value for exogenous
stochastic variables, since it is the only possible value.

This steady state will be used as the initial condition at all the
periods preceeding the first simulation period for the two possible
types of simulations in stochastic mode:

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@item
in @code{stoch_simul}, if the @code{periods} options is specified

@item
in @code{forecast} (in this case, note that it is still possible to
modify some of these initial values with @code{histval})
@end itemize

@examplehead

@example
initval;
c = 1.2;
k = 12;
x = 1;
end;

steady;
@end example

@end deffn

@deffn Block endval ;

@descriptionhead

This block is terminated by @code{end;}, and contains lines of the
form:
@example
@var{VARIABLE_NAME} = @var{EXPRESSION};
@end example

The @code{endval} block makes only sense in a determistic model, and
serves two purposes.

First, it sets the terminal conditions for all the periods succeeding
the last simulation period.

Second, it provides initial guess values at all the simulation dates
for the non-linear solver implemented in @code{simul}.

For this last reason, it necessary to provide values for all the
endogenous variables in an @code{endval} block (even though,
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@code{endval} block, a zero value is assumed.

Note that if the @code{endval} block is immediately followed by a
@code{steady} command, its semantics is changed. The @code{steady}
command will compute the steady state of the model for all the
endogenous variables, assuming that exogenous variables are kept
constant to the value declared in the @code{endval} block, and using
the values declared for the endogenous as initial guess values for the
non-linear solver. An @code{endval} block followed by @code{steady} is
formally equivalent to an @code{endval} block with the same values for
the exogenous, and with the associated steady state values for the
endogenous.

@examplehead

@example
var c k;
varexo x;
@dots{}
initval;
c = 1.2;
k = 12;
x = 1;
end;

steady;

endval;
c = 2;
k = 20;
x = 2;
end;

steady;
@end example

The initial equilibrium is computed by @code{steady} for @code{x=1},
and the terminal one, for @code{x=2}.

@end deffn

@deffn Block histval ;

@descriptionhead

In models with lags on more than one period, the @code{histval} block
permits to specify different historical initial values for different
periods.

This block is terminated by @code{end;}, and contains lines of the
form:
@example
@var{VARIABLE_NAME}(@var{INTEGER}) = @var{EXPRESSION};
@end example

@var{EXPRESSION} is any valid expression returning a numerical value
and can contain already initialized variable names.

By convention in Dynare, period 1 is the first period of the
simulation. Going backward in time, the first period before the start
of the simulation is period @code{0}, then period @code{-1}, and so on.

If your lagged variables are linked by identities, be careful to
satisfy these identities when you set historical initial values.

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Variables not initialized in the @code{histval} block are assumed to
have a value of zero at period 0 and before. Note that this behavior
differs from the case where there is no @code{histval} block, where all
variables are initialized at their steady state value at period 0 and
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before (except when a @code{steady} command doesn't follow an
@code{initval} block).
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@examplehead

@example
var x y;
varexo e;

model;
x = y(-1)^alpha*y(-2)^(1-alpha)+e;
@dots{}
end;

initval;
x = 1;
y = 1;
e = 0.5;
end;

steady;

histval;
y(0) = 1.1;
y(-1) = 0.9;
end;
@end example

@end deffn

@deffn Command resid ;

This command will display the residuals of the static equations of the
model, using the values given for the endogenous in the last
@code{initval} or @code{endval} block (or the steady state file if you
provided one, @pxref{Steady state}).

@end deffn


@deffn Command initval_file (filename = @var{FILENAME});

@descriptionhead

In a deterministic setup, this command is used to specify a path for
all endogenous and exogenous variables. The length of these paths must
be equal to the number of simulation periods, plus the number of leads
and the number of lags of the model (for example, with 50 simulation
periods, in a model with 2 lags and 1 lead, the paths must have a
length of 53). Note that these paths cover two different things:

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@itemize
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@item
the constraints of the problem, which are given by the path for
exogenous and the initial and terminal values for endogenous

@item
the initial guess for the non-linear solver, which is given by the
path for endogenous variables for the simulation periods (excluding
initial and terminal conditions)
@end itemize

The command accepts three file formats:

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@item
M-file (extension @file{.m}): for each endogenous and exogenous
variable, the file must contain a row vector of the same name.

@item
MAT-file (extension @file{.mat}): same as for M-files.

@item
Excel file (extension @file{.xls}): for each endogenous and exogenous,
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the file must contain a column of the same name (supported under Octave
if the @uref{http://octave.sourceforge.net/io/,io} and
@uref{http://octave.sourceforge.net/java/,java} packages from
Octave-Forge are installed, along with a
@uref{http://www.java.com/download,Java Runtime Environment}).
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@end itemize

@customhead{Warning}

The extension must be omitted in the command argument. Dynare will
automatically figure out the extension and select the appropriate file
type.

@end deffn

@node Shocks on exogenous variables
@section Shocks on exogenous variables

In a deterministic context, when one wants to study the transition of
one equilibrium position to another, it is equivalent to analyze the
consequences of a permanent shock and this in done in Dynare through
the proper use of @code{initval} and @code{endval}.

Another typical experiment is to study the effects of a temporary
shock after which the system goes back to the original equilibrium (if
the model is stable@dots{}). A temporary shock is a temporary change of
value of one or several exogenous variables in the model. Temporary
shocks are specified with the command @code{shocks}.

In a stochastic framework, the exogenous variables take random values
in each period. In Dynare, these random values follow a normal
distribution with zero mean, but it belongs to the user to specify the
variability of these shocks. The non-zero elements of the matrix of
variance-covariance of the shocks can be entered with the @code{shocks}
command. Or, the entire matrix can be direclty entered with
@code{Sigma_e} (this use is however deprecated).

If the variance of an exogenous variable is set to zero, this variable
will appear in the report on policy and transition functions, but
isn't used in the computation of moments and of Impulse Response
Functions. Setting a variance to zero is an easy way of removing an
exogenous shock.

@deffn Block shocks ;

@customhead{In deterministic context}

For deterministic simulations, the @code{shocks} block specifies
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temporary changes in the value of exogenous variables. For
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permanent shocks, use an @code{endval} block.

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The block should contain one or more occurrences of the following
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group of three lines:

@example
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var @var{VARIABLE_NAME};
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periods @var{INTEGER}[:@var{INTEGER}] [[,] @var{INTEGER}[:@var{INTEGER}]]@dots{};
values @var{DOUBLE} | (@var{EXPRESSION})  [[,] @var{DOUBLE} | (@var{EXPRESSION}) ]@dots{};
@end example

It is possible to specify shocks which last several periods and which can
vary over time. The @code{periods} keyword accepts a list of
several dates or date ranges, which must be matched by as many shock values
in the @code{values} keyword. Note that a range in the