> On 26 Jan 2024, at 3:03 PM, mich...@paraffinalia.co.uk wrote: > > On 2024-01-23 18:09, Junchao Zhang wrote: >> Do you have an example to reproduce it? >> --Junchao Zhang > > I have put a minimum example on github: > > https://github.com/mjcarley/petsc-test > > It does seem that the problem occurs if I do not use the PETSc interface to > do a matrix multiplication. > > In the original code, the PETSc matrix is a wrapper for a Fast Multipole > Method evaluation; in the minimum example I have simulated this by using an > array as a matrix. The sample code generates a randomised matrix A and > reference solution vector ref, and generates a right hand side > > b = A*ref > > which is then supplied as the right hand side for the GMRES solver. If I use > the PETSc matrix multiplication, the solver behaves as expected; if I > generate b directly from the underlying array for the matrix, I get the result
You should not use VecGetArrayRead() if you change the Vec, but instead, VecGetArrayWrite(). Does that solve the issue? Thanks, Pierre > 0 KSP Residual norm < 1.e-11 > Linear solve converged due to CONVERGED_ATOL iterations 0
