[petsc-users] Running an iterative method for a large number of iterations: Possible blow up?

Gaurish Telang gaurish108 at gmail.com
Fri Feb 18 01:26:18 CST 2011


I was trying to use LSQR algorithm for solving a least squares problem of
size 2683x1274. I notice that if I allow the iterative method to run for a
large number of iterations
after it has converged (i.e. output of -ksp_monitor KSPresidualnorm seems
constant upto the 4th digit) , some numbers in the answer vector seem to get
inordinately large.

I seem to get my answer comparable to Matlab after 951 iterations, but when
I increase the number of iterations to 10000 some numbers seem very large.

Is this expected? Also, how do I terminate my iteration when my residual
norm  seems constant?

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