Fiscal Multiplier in Dynare

How do you calculate fiscal multipliers in dynare?

And the multiplier contains a shock which does not appear in the model setting. I don’t understand this part.
FISCAL MULTIPLIERS IN RECESSIONS.pdf (1.6 MB)
Any guidance would be much appreciated.

The exact computation depends on the exact type of simulation you are conducting. But the equation above is just the definition of a generalized IRF in that it compares two different simulations paths.