[petsc-users] EPS iteration number

[Jose E. Roman]

> El 17/9/2015, a las 21:33, Xujun Zhao <xzhao99 at gmail.com> escribió:
> 
> Hi Jose,
> 
> This is only a very simple test. 2 outer iterations perform 24 MatMult operation, which means I have to solve a Finite element system with millions of DOFs for 24 times. This is only for a polymer system with two beads. For a polymer chain with hundreds of beads and springs, I need more outer iterations to get its max/min eigenvalues, which means I have to perform more computations of the finite element system. Those solves happen only for one time step. When polymer beads move, I need to redo everything. 
> 
> In other words, the eigenvalues (max and min) have to be solved every time step or every several time steps. Therefore, it is very expensive! My question is that if It is possible to use the eigenvalues obtained from last time step as an initial guess to accelerate the convergence. Thank you for your help.
> 
> Xujun

Eigenvalues cannot be used as initial guess. You can try passing the previous eigenvector with EPSSetInitialSpace(), but there is no guarantee it is effective to improve convergence.

Jose