As far as I understand, tol sets the relative residual tolerance for MinRes, GMRes and CG solvers. Is this the true residual or the preconditioned residual? I’m assuming it’s the preconditioned residual, but I was hoping to get some confirmation on this. If it is the preconditioned residual, is there a way to print out the true residual as well?
yes, should be. I think the easiest way to do such things is just to copy the krylovspace.py file from ngsolve and modify as you like and use your copy. I think the cgsolver is like 100-200 lines of code and can be stripped down to probably 50.
Best
Christopher