[petsc-users] KSP solver increases the solution time

[Alejandro Marcos Aragón]

Hi Jed, thanks for replying. In fact, the problem I sent the results from is a dynamic problem of a simply supported beam subjected to a constant load at the center, so I'm integrating in time. The material is linear elastic so the stiffness matrix doesn't change in non-zero structure. Of course the right hand side changes, but I don't think this is the problem because at some point it takes it goes back to just a few iterations to solve. The behavior is cyclic, but I don't understand the reason for this. I've noticed the same behavior of the solver also in quasi-static problems (increasing the load gradually but not integrating over time).

Alejandro M. Aragón

On Apr 26, 2011, at 9:52 AM, Jed Brown wrote:

> 2011/4/26 Alejandro Marcos Aragón <alejandro.aragon at gmail.com>
> As you can see, the second iteration takes more than 40 seconds to solve. Could some explain why this is happening and why he number of iterations is increasing dramatically between solves?
> 
> What has changed between solves? If this is part of a nonlinear problem, it might have just gotten harder to solve. If the linear system is the same, the right hand side for the first problem was probably degenerate (roughly speaking, having significant energy in only a few Krylov modes).

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