Heteroschedastic filter and smoother

Implements heteroschedastic filters, where shocks standard error may unexpectedly change in every period. shocks standard deviation may be set/modified in each observed period by

• a scale factor, i.e. if std0 is the usual standard error for shock1, std(shock1|t)=std0(shock1)*scale(t)
• an imputed value: std(shock1|t)=value(t)

Preprocessor requirements:

1. new option heteroschedastic_filter for estimation and evaluate_smoother: triggers the field options_.heteroschedastic_filter.
2. new block heteroschedastic_shocks:

heteroschedastic_shocks;

var e1;
periods 86:97;
scale 0.5 0.5 (zeros(1,10));

var e2;
periods 86:97;
value 0.04 0.04 (repmat(0.01,[1 10]));
end;

var e3;
periods 86:87;
value 0.04 0.04 ;
end;

var e3;
periods 88:97;
scale 0;
end;

that triggers the following fields in M_:

M_.heteroschedastic_shocks.Qhet.e1.time_scale=86:97;
M_.heteroschedastic_shocks.Qhet.e1.scale=[0.5 0.5 zeros(1,10)];

M_.heteroschedastic_shocks.Qhet.e2.time_value=86:97;
M_.heteroschedastic_shocks.Qhet.e2.value=[0.04 0.04 repmat(0.01,[1 10])];

M_.heteroschedastic_shocks.Qhet.e3.time_value=86:87;
M_.heteroschedastic_shocks.Qhet.e3.value=[0.04 0.04];

M_.heteroschedastic_shocks.Qhet.e3.time_scale=88:97;
M_.heteroschedastic_shocks.Qhet.e3.scale=0;

this input info is the handled in dynare_estimation_init, by filling in arrays of size [M_.exo_nbr x options_.nobs]

M_.heteroschedastic_shocks.Qscale 
M_.heteroschedastic_shocks.Qvalue

Users may not define, for the same shock and the same period, scale AND value. the can define for the same shock, scale and values for different periods.