[petsc-users] Why the convergence is much slower when I use two nodes

[Barry Smith]

   You need to provide more information. What is the output of -ksp_view? and -log_view? for both cases

> On Jun 12, 2017, at 7:11 PM, Ji Zhang <gotofd at gmail.com> wrote:
> 
> Dear all, 
> 
> I'm a PETSc user. I'm using GMRES method to solve some linear equations. I'm using boundary element method, so the matrix type is dense (or mpidense). I'm using MPICH2, I found that the convergence is fast if I only use one computer node; and much more slower if I use two or more nodes. I'm interested in why this happen, and how can I improve the convergence performance when I use multi-nodes. 
> 
> Thanks a lot. 
> 
> 此致
>     敬礼
> 张骥（博士研究生）
> 北京计算科学研究中心 
> 北京市海淀区西北旺东路10号院东区9号楼 （100193）
> 
> Best, 
> Regards, 
> Zhang Ji, PhD student
> Beijing Computational Science Research Center 
> Zhongguancun Software Park II, No. 10 Dongbeiwang West Road, Haidian District, Beijing 100193, China