[petsc-users] Infinite or not-a-number generated in norm!

[Dominik Szczerba]

> I suspect your custom preconditioner is computing NaN for the call to the
> inner solver. Run with -fp_trap -start_in_debugger to see where NaN was
> first generated.

Very useful hint that with -fp_trap. I get trapped at:

Program received signal SIGFPE, Arithmetic
exception.0x00000000010fad4e in hypre_BoomerAMGRelax (A=0x1b56e9a0,
f=0x195487b0,     cf_marker=0x692b900, relax_type=6, relax_points=1,
relax_weight=1,     omega=1, l1_norms=0x0, u=0xb0f8aa0,
Vtemp=0x18fd1900, Ztemp=0x0)    at par_relax.c:19251925
      u_data[i] = res / A_diag_data[A_diag_i[i]];
with  res = -2.4683099805590231e+303 and A_diag_data[A_diag_i[i]] =
9.287739686222747e-06. The full backtrace goes through many boomeramg
lines to point back at the end to my code where (in a custom
preconditioner) I solve a linear system with KSPGMRES and
PCHYPRE/boomeramg. I guess I will proceed now with inspecting the
values by hand, but if there still are some useful Petsc tricks I am
eager to hear.