[Trilinos-Users] Convergence criteria in Belos

erhan turan turane at gmail.com
Thu Apr 12 06:43:05 MDT 2012

Dear All,

I have difficulty in defining a convergence criteria other than the
relative residual test in Belos. In AztecOO, we have the option to select
among various convergence options using "AZ_conv": relative, absolute
residual test or any others. Specifically what I need is AZ_rhs where the
comparison is made against the 2-norm of RHS (i.e norm of b in Ax=b).
Normally, if you have a solver that works with relative residuals only,
then you might multiply your convergence tolerance with the initial norm
and use that modified tolerance as the new criteria. And even in my case,
it is still possible to modify the tolerance further with norm of b. That's
fine but I don't want that.

If these options are somewhat available but hidden within Belos, I would
like to hear that. If not, do you have any suggestions? I believe,
statusTestNorm could be replaced somehow using the
statusTestOutputFactory.hpp file but not sure how to implement it. I was
not able to relate it to AztecOO_StatusTest class as suggested in
DesignRequirements.txt in doc folder of Belos source. I also noticed that
in some Belos examples, there are additional operations after Solve() to
calculate the residual explicitly. Those cases gave me the impression that
only relative residual is available in Belos even if there is this belos
option  "Explicit Residual Test" which is handy in left preconditioned
problems. It would be nice of you if the residual operations in Belos are
clarified somehow.


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