Add interface to set zero_moments_tolerance

Useful in identification and method_of_moments to set the tolerance which replaces very small numbers by hard zeros in unconditional second moments. Merge request for that will follow after this is merged in the preprocessor.

changed milestone to %5.x

added macroprocessor label

Actually there is a cutoff option to the model block which serves a similar purpose: it is used to determine the threshold under which a numerically small derivative is considered as a real zero (and thus that the corresponding variable does not enter the equation in the block decomposition).

I wonder whether we should reuse that name, even though it would be in a slightly different context?

I don't really mind, but cutoff is declared a <DYNARE_BLOCK>cutoff {return token::CUTOFF;}, whereas the proposed zero_moments_tolerance is a <DYNARE_STATEMENT>zero_moments_tolerance {return token::ZERO_MOMENTS_TOLERANCE;}. Also, in disp_moments.m we already use zero_moments_tolerance, which does exactly the same to what I want to do in pruned_state_space.m. So I would rather stick with zero_moments_tolerance if that is okay with you?

The block vs statement thing is easy to solve technically. And the already existing zero_moments_tolerance is not user-visible (it is not part of the .mod language).

But I agree that the name you propose is more explicit than cutoff. And that both options do not serve exactly the same purpose. So I'll merge this.

merged

mentioned in commit 50782694