Creates a matrix with a uniform value along the diagonal
comm - MPI communicator
m - number of local rows (or
PETSC_DECIDEto have calculated if M is given) This value should be the same as the local size used in creating the y vector for the matrix-vector product y = Ax.
n - This value should be the same as the local size used in creating the x vector for the matrix-vector product y = Ax. (or PETSC_DECIDE to have calculated if N is given) For square matrices n is almost always m.
M - number of global rows (or
PETSC_DETERMINEto have calculated if m is given)
N - number of global columns (or
PETSC_DETERMINEto have calculated if n is given)
diag - the diagonal value
J - the diagonal matrix
Only supports square matrices with the same number of local rows and columns