[petsc-users] GAMG and linear elasticity

[Mark F. Adams]

On Sep 1, 2013, at 8:37 AM, Tabrez Ali <stali at geology.wisc.edu> wrote:

> I am using solid elements and here's what I get for the smallest problem with -pc_type svd -pc_svd_monitor
> 
>    SVD: condition number 4.184203727999e+13, 0 of 2187 singular values are (nearly) zero
>    SVD: smallest singular values: 9.975131304660e-01 9.979349868120e-01 9.986761984005e-01 9.993267254639e-01 9.996135846381e-01
>    SVD: largest singular values : 3.933977100529e+13 3.933977100529e+13 4.162059658259e+13 4.162059658259e+13 4.173798159224e+13
> 

This is a very large condition number for a "vanilla 3D linear elasticity problem" [there are no rotations].

The 5 lowest values are very similar … are you sure you have sufficient BCs?

> Tabrez
> 
> On 08/31/2013 03:06 PM, Umut Tabak wrote:
>> On 08/31/2013 06:25 PM, Tabrez Ali wrote:
>>> Hello
>>> 
>>> So I used PCSetCoordinates and now GAMG seems to work really well in that the number of iterations are relatively constant. Here are the number of iterations on 4 cores
>>> 
>>> DOF       ASM    GAMG
>>> 2187       15     22
>>> 14739      26     22
>>> 107811     51     29
>> 
>> Hi,
>> 
>> Just curious, what is the approximate condition number of this matrix, is that modelled with domain elements like solids or thin elements like shells?
>> 
>> Best,
>> U.
>