[petsc-users] large number of iteration.

[Smith, Barry F.]

> On Aug 5, 2018, at 9:38 PM, Josh L <ysjosh.lo at gmail.com> wrote:
> 
> Hi,
> 
> I am using GRMES to solve the linear systems within Newton Raphson. 
> I am using finite element method to solve fracture problem with phase field method.(the formulation gives symmetric but indefinite hessian so can't use CG) 

    What exact equations are you using for the phase field method?

     With the direct LU solver roughly how many iterations does your Newton's method take?


   Barry

> 
> The total iteration number to solve one linear system is often very large( > 2000) even for a small sized problem(120K degree of freedom). I've tried different preconditioner, but it doesn't help a lot.  I have checked my hessian and right hand side, and sure they are correct. 
> 
> I think it might stem from the great difference in element size(max/min=100) and damage stiffness around crack. 
> 
> Anyone has idea to reduce the number of iteration?
> 
> Now, I get away with it by using LU, which is not ideal for large size problem (I will have to run it in the future)
> 
> 
> Thanks,
> Josh
>