# [Trilinos-Users] Belos relative residual question

Alicia M Klinvex aklinvex at purdue.edu
Tue Jan 29 14:05:33 MST 2013

```Hello all,

I've been using the iterative solvers in Belos (without preconditioning), and I have a question.  I'm trying to solve a linear system with a matrix from the Tim Davis collection (n~1.5 million, SPD, infinity norm~1e13, condition number unknown).  I get the following output:

Belos::StatusTestGeneralOutput: Passed
(Num calls,Mod test,State test): (1001, 1, Passed)
Passed.......OR Combination ->
Failed.......Number of Iterations = 1000 == 1000
Unconverged..(2-Norm Imp Res Vec) / (2-Norm Res0)
residual [ 0 ] = 3.529270e+01 > 1.000000e-09
residual [ 1 ] = 3.315928e+01 > 1.000000e-09
residual [ 2 ] = 3.379295e+01 > 1.000000e-09
residual [ 3 ] = 3.545595e+01 > 1.000000e-09
residual [ 4 ] = 3.886068e+01 > 1.000000e-09
residual [ 5 ] = 3.623544e+01 > 1.000000e-09
residual [ 6 ] = 3.766880e+01 > 1.000000e-09
residual [ 7 ] = 3.573129e+01 > 1.000000e-09
residual [ 8 ] = 3.265649e+01 > 1.000000e-09
residual [ 9 ] = 3.407210e+01 > 1.000000e-09
residual [ 10 ] = 3.412164e+01 > 1.000000e-09
residual [ 11 ] = 3.268996e+01 > 1.000000e-09
residual [ 12 ] = 3.239391e+01 > 1.000000e-09
residual [ 13 ] = 3.618865e+01 > 1.000000e-09
residual [ 14 ] = 3.389451e+01 > 1.000000e-09
residual [ 15 ] = 3.418135e+01 > 1.000000e-09

Any ideas as to why I might be getting a relative residual of 35?  As always, code is available on request.

Thank you,
Alicia

```