[petsc-users] slepc on 1D row distributed matrix

Jose E. Roman jroman at dsic.upv.es
Wed May 31 15:26:40 CDT 2017

> El 31 may 2017, a las 21:46, Kannan, Ramakrishnan <kannanr at ornl.gov> escribió:
> Hello,
> I have got a sparse 1D row distributed matrix in which every MPI process owns an m/p x n of the global matrix mxn.  I am running NHEP with krylovschur on it. It is throwing me some wrong error. For your reference, I have attached the modified ex5.c in which I SetSizes on the matrix to emulate the 1D row distribution and the log file with the error.
> In the unmodified ex5.c, for m=5, N=15, the local_m and the local_n is 3x3. How is the global 15x15 matrix distributed locally as 3x3 matrices? When I print the global matrix, it doesn’t appear to be diagonal as well. 
> If slepc doesn’t support sparse 1D row distributed matrix, how do I need to redistribute it such that I can run NHEP on this.
> -- 
> Regards,
> Ramki
> <ex5.c><slepc.o607511>

As explained in the manpage, the local columns size n must match the local size of the x vector, so it must also be N/mpisize

But be warned that your code will not work when N is not divisible by mpisize. In that case, global and local dimensions won't match.

Setting local sizes is not necessary in your case, since by default PETSc is already doing a 1D block-row distribution.


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