I am guessing that you are creating a matrix, adding to it, finalizing it ("assembly"), and then adding to it again, which is fine, but you are adding new non-zeros to the sparsity pattern.

If this is what you want then you can tell the matrix to let you do that.

Otherwise you have a bug.

Mark

On Tue, Dec 19, 2023 at 9:50 PM Shatanawi, Sawsan Muhammad via petsc-users <petsc-users@mcs.anl.gov> wrote:

Hello everyone,

I hope this email finds you well.

My Name is Sawsan Shatanawi, and I am currently working on developing a Fortran code for simulating groundwater flow in a 3D system. The code involves solving a nonlinear system, and I have created the matrix to be solved using the PCG solver and Picard iteration. However, when I tried to assign it as a PETSc matrix I started getting a lot of error messages.

I am kindly asking if someone can help me, I would be happy to share my code with him/her.

Please find the attached file contains a list of errors I have gotten

Thank you in advance for your time and assistance.

Best regards,

Sawsan