!if

Choose a branch of code based on logical condition

Syntax with else and elseif clauses

!if Condition1
    Block1
!elseif Condition2
    Block2
!elseif Condition3
...
!else
    Block3
!end

Syntax with an else clause only

!if Condition1
    Block1
!else
    Block2
!end

Syntax without an else clause

!if Condition
    Block1
!end

Description

The !if command works the same way as its counterpart in the Matlab programming language.

Use the command to create multiple branches or versions of the model source code. Whether a block of code in a particular branch is used or discarded, depends on the condition after the opening !if command and the conditions after subsequent !elseif commands if present. The condition must be a Matlab expression that evaluates to true or false. The condition can refer to model parameters, or to other fields included in the database passed in through the option 'assign=' in the model function.

Example

!if B < Inf
    % This is a linearised sticky-price Phillips curve.
    pi = A*pi{-1} + (1-A)*pi{1} + B*log(mu*rmc);
!else
    % This is a flexible-price mark-up rule.
    rmc = 1/mu;
!end

If you set the parameter B to Inf in the parameter database when reading in the model file, then the flexible-price equatio, rmc = 0, is used and the Phillips curve equation discarded. To use the Phillips curve equation instead, you need to re-read the model file with B set to a number other than Inf. In this example, B needs to be, obviously, declared as a model parameter.

Example

!if exogenous == true
    x = y;
!else
    x = rho*x{-1} + epsilon;
!end

When reading the model file in, create a parameter database, include at least a field named exogenous in it, and use the 'assign=' option to pass the database in. Note that you do not need to declare exogenous as a parameter in the model file.

P = struct( );
P.exogenous = true;
...
m = model('my.model','assign=',P);

In this case, the model will contain the first equation, x = rho*x{-1} + epsilon; will be used, and the other discarded. To use the other equation, x = y, you need to re-read the model file with exogenous set to false:

P = struct( );
P.exogenous = false;
...
m = model('my.model','assign=',P);

You can also use an abbreviate syntax to assign control parameters when readin the model file; for instance

m = model('my.model','exogenous=',true);