Equations tags

The feature was introduced in Dynare v.4.1. It allows user to attach arbitrary informations to each equation and to recover them at runtime. It is particularly useful to specify names of equations but can also be used to introduce other informations in the model. Tags are stored in a special structure M_.equations_tags. Currently, equations tags are not used by any Dynare code from the portfolio module but they can be very useful for handwritten code.

Flagging equations with tags

Before each equation in the modfile, the user can specify a list pairs (key,values) were key is any identifier and value a single-quoted string. This is demonstrated by the following example :

...preamble

model;

[name = 'Budget constraint']
c + k = k^theta*A;

[name = 'Euler condition', euler_var='k']
beta*(c(1)/c)^(-sigma)*theta*k^(theta-1)*A(1) = 1;

[name = 'Specification of shocks', type='exogenous']
log(A) = rho*log(A(-1))  + epsilon;

end;
...conclusion

In this simple example, we have given a name to each equation. We have also added the name of the variable used to derive the Euler equation and have specified that last equation is exogenous.

Usecases

Find the equation corresponding to nonzero residuals

It is common to be looking for the steady state of a given set of equations. The command 'resid' included in Dynare, can be used to print the residuals and see which equations are met at the steady-state. However, this command helps to find the numbers of the faulty equations. When the number of equations is big, it is easier to use the command resid_with_names resid_with_names.m , which will also print the value of a specific key for all the equations. For instance, calling resid_with_names('name') for the (fictive) previous model will output something like

Eq (1) : 0 : Budget constraint
Eq (2) : 0.1 : Euler condition
Eq (3) : 0 : Specification of shocks

making it easy to figure out the faulty equation.

Details about the implementation

• Add general labels to equations. In the current prototype a list of key-values pair can be written in brackets before each equation :

[key='value',key='value',...] y = y + 1;

One may want to attach values of any type to an equation. Currently, only strings of characters are recognized but we ask the user to specify users to enter quoted strings nevertheless. Type of keys should also be restricted so that they can be used as fields in matlab structures if needed, i.e. no numeric character, no space,...

• Structure in the preprocessor is the same as in Matlab and mimics a database table : an array with 3 columns. It is stored in M_.equations_tags as in :

M_.equations_tags = {
    1 'name' 'First equation';
    2 'name' 'Second equation';
    2 'portfolio' 'true';
};

• It is easy to query this table in matlab as follows

tags = M_.equations_tags;
tags(cell2mat(tags(:,1))==2,2:3) % all tags for equation 2
tags(strmatch('name',tags(:,2)),[1 3]) % a vector with equations numbers and associated names