[petsc-dev] Error in MatGetDiagonal_Shell?

[Stefano Zampini]

> On Apr 30, 2018, at 3:14 AM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
> 
> 
>   I don't understand
> 
>    The code has
> 
>  ierr = MatGetDiagonal(A,W2);CHKERRQ(ierr);
>  ierr = VecView(W2,viewer);CHKERRQ(ierr);
> 
>   the output from this VecView seems to match the diagonal of the matrix printed earlier.
> 
>> On Apr 29, 2018, at 10:02 AM, Stefano Zampini <stefano.zampini at gmail.com> wrote:
>> 
>> By looking at src/mat/examples/tests/output/ex88_1.out, it seems that the output of MatGetDiagonal is wrong for MATSHELL. 
>> 
>> it should be 
>> 2.96782e+08
>> 1.41731e+09
>> and not (as computed) 
>> 1.10918e+08
>> 2.06459e+08
> 
>   What do you mean "as computed"? The output file does not contain
>> 1.10918e+08
>> 2.06459e+08
> anywhere.
> 
>   Are you modifying the example and running it again to get the incorrect value?

Yes, my bad. I did not explain it correctly
From maint, if you just run ex88 you will get the incorrect output, which is not caught in the nightlyies because floating point values are completely ignored.

[szampini at localhost tests]$ ./ex88
Matrix of type: shell
Mat Object: 1 MPI processes
  type: seqdense
2.9678190300000000e+08 3.9288008100000000e+08 
6.1374683500000000e+08 1.4173141580000000e+09 
Vec Object: 1 MPI processes
  type: seq
3.92973e+19
8.54197e+19
Vec Object: 1 MPI processes
  type: seq
1.10918e+08
2.06459e+08
MatDiagonalSet not tested on MATSHELL
….

> 
>  Barry
> 
>> 
>> -- 
>> Stefano
>