Specification of Inverse Gamma Priors

Dynare help (legacy posts)
1

Hi Dynare community,

I am trying to specify the following priors

  1. Inverse gamma with mode = 1.5 and degrees of freedom = 4
  2. Inverse gamma with mode = 0.001 and degrees of freedom = 2

I was wondering how I might do this since dynare requires I specify the mean and variance?

Regards,

2

Hi,

The trick is that (with recent version of dynare >=4.1) it is possible to call a function inside the estimated_params block. I find more intuitive to define a non symmetric prior with the mode and the standard deviation, so instead of declaring a number for the prior mean I call a function computing the mean from the mode and the standard deviation (or the variance). This is done (for all prior shapes) in the matlab function
mode_and_variance_to_mean (this function is in the subfolder distributions of the dynare’s matlab folder). You can write a function computing the mean and the standard deviation from the mode and the degrees of freedom (I am not sure it’s possible to obtain the mapping analitically).

Best, Stéphane.