Commit 70ccb1d0 authored by Sébastien Villemot's avatar Sébastien Villemot
Browse files

Documentation of new differentiate_forward_vars option

Ref #351
parent d0510261
......@@ -1555,6 +1555,22 @@ belong to the set of feedback variables.
@item no_static
Don't create the static model file. This can be useful for models which
don't have a steady state.
@item differentiate_forward_vars
Tells Dynare to create a new auxiliary variable for each endogenous
variable that appears with a lead, such that the new variable is the
time differentiate of the original one. More precisely, if the model
contains @code{x(+1)}, then a variable @code{AUX_DIFF_VAR} will be
created such that @code{AUX_DIFF_VAR=x-x(-1)}, and @code{x(+1)} will
be replaced with @code{x+AUX_DIFF_VAR(+1)}.
This option can useful for some deterministic simulations where
convergence is hard to obtain. Bad values for terminal conditions in
the case of very persistent dynamics or permanent shocks can hinder
correct solutions or any convergence. The new differentiated variables
have obvious zero terminal conditions (if the terminal condition is a
steady state) and this in many cases helps convergence of simulations.
@end table
@customhead{Example 1: elementary RBC model}
......@@ -1725,6 +1741,11 @@ 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).
The last type of auxiliary variables is introduced by the
@code{differentiate_forward_vars} option of the @code{model} block.
The new variables take the form @code{AUX_DIFF_FWRD_@var{i}}, and are
equal to @code{x-x(-1)} for some endogenous variable @code{x}.
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
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