Addressing Stan speed claims in general

[yizhang]

@Bob_Carpenter

What’s a CFD simulation?

Computational Fluid Dynamics. What I’ve done for PDE is a proof of concept, more realistic work has been started by @IvanYashchuk in his petsc project Using PETSc library together with Stan. I don’t think it’s meaningful to jump into large-scale 3rd party simulator before we can clean up Stan’s MPI framework, as @IvanYashchuk has realized.