Print iterative solver information

[sangallidavide]

Dear developers, would you have suggestions on how to modify the following code:

https://gitlab.com/lumen-code/lumen/-/blob/yambo-devs-main/src/linear_algebra/SERIAL_HERMITIAN_chase.F

in order to get info about the iterative procedure (I'm assuming cchase is performing iteration to converge the requested number of eigenvalues)

[brunowu]

Hi Davide,

currently there is no built-in runtime option in ChASE to enable or disable detailed prints of the iterative procedure (e.g., residual history, filtering steps, locking information).

If you want to get insight into the iterations performed inside cchase, the practical way at the moment is to recompile ChASE with the CHASE_OUTPUT flag enabled. This activates the internal verbose output that reports convergence progress and related iteration data.

Concretely, you can add:

-DCHASE_OUTPUT

to your compilation flags when building ChASE.

If you need finer-grained control (e.g., printing only residual norms or only at specific iterations), that would require introducing additional logging hooks in the solver loop. Let us know if that would be useful for your workflow, and we can discuss a cleaner interface.