[petsc-dev] Meaning of PETSc matrices with zero rows but nonzero columns?

[Jed Brown]

Stefano Zampini <stefano.zampini at gmail.com> writes:

> If A is 0x8 and B is 8x5 then C is correct to be of size 0x5. The rows and columns of the resulting matrix have to follow the rules.

Right, I think if you said C is 0x0 (which seems like Richard's proposal), you'd need to relax shape compatibility logic in many places, including in ways that might produce confusing errors.

Richard, what is the hardship in preserving the shape relations?