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Declarations of variables and parameters are made with the following commands:
Description
This required command declares the endogenous variables in the model. See section Conventions, for the syntax of VARIABLE_NAME and MODEL_EXPRESSION. Optionally it is possible to give a LaTeX name to the variable or, if it is nonstationary, provide information regarding its deflator.
var commands can appear several times in the file and Dynare will
concatenate them.
Options
If the model is nonstationary and is to be written as such in the
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.
deflator = MODEL_EXPRESSIONThe expression used to detrend an endogenous variable. All trend
variables, endogenous variables and parameters referenced in
MODEL_EXPRESSION must already have been declared by the
trend_var, var and parameters commands.
Example
var c gnp q1 q2; var(deflator=A) i b; |
Description
This optional command declares the exogenous variables in the model. See section Conventions, for the syntax of 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.
varexo commands can appear several times in the file and Dynare
will concatenate them.
Example
varexo m gov; |
Description
This optional command declares exogenous deterministic variables in a stochastic model. See Conventions, for the syntax of 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 stoch_simul will compute the
rational expectation solution adding future information to the state
space (nothing is shown in the output of stoch_simul) and
forecast will compute a simulation conditional on initial
conditions and future information.
varexo_det commands can appear several times in the file and
Dynare will concatenate them.
Example
varexo m gov; varexo_det tau; |
Description
This command declares parameters used in the model, in variable initialization or in shocks declarations. See Conventions, for the syntax of PARAMETER_NAME. Optionally it is possible to give a LaTeX name to the parameter.
The parameters must subsequently be assigned values (see section Parameter initialization).
parameters commands can appear several times in the file and
Dynare will concatenate them.
Example
parameters alpha, bet; |
Description
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 ‘.mod’ file: the type change is effective after, but also
before, the 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.
Example
var y, w; parameters alpha, bet; … change_type(var) alpha, bet; change_type(parameters) y, w; |
Here, in the whole model file, alpha and beta will be
endogenous and y and w will be parameters.
Description
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 k(-1), and the law of motion of
capital must be written:
k = i + (1-delta)*k(-1) |
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 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.
Example
The following two program snippets are strictly equivalent.
Using default Dynare timing convention:
var y, k, i; … model; y = k(-1)^alpha; k = i + (1-delta)*k(-1); … end; |
Using the alternative timing convention:
var y, k, i; predetermined_variables k; … model; y = k^alpha; k(+1) = i + (1-delta)*k; … end; |
Description
This optional command declares the trend variables in the model. See section Conventions, for the syntax of MODEL_EXPRESSION and 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 model block. The trend_var
command must appear before the var command that references the
trend variable.
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
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
growth_factor keyword. All endogenous variables and
parameters referenced in MODEL_EXPRESSION must already have been
declared by the var and parameters commands.
Example
trend_var (growth_factor=gA) A; |
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