Hi, la, 2008-03-01 kello 16:43 -0300, Lisandro Dalcin kirjoitti: > I want to comment some extrange stuff I'm experiencing with numpy. > Please, let me know if this is expected and known. > > I'm trying to solve a model nonlinear PDE, 2D Bratu problem (-Lapacian > u - alpha * exp(u), homogeneus bondary conditions), using the simple > finite differences with a 5-point stencil. > > I implemented the finite diference scheme in pure-numpy, and also in a > F90 subroutine, next wrapped with f2py. > > Next, I use PETSc (through petsc4py) to solve the problem with a > Newton method, a Krylov solver, and a matrix-free technique for the > Jacobian (that is, the matrix is never explicitelly assembled, its > action on a vector is approximated again with a 1st. order finite > direrence formula). > > And the, surprise! The pure-numpy implementation accumulates many more > inner linear iterations (about 25%) in the complete nonlinear solution > loop than the one using the F90 code wrapped with f2py.
A silly question: did you check directly that the pure-numpy code and the F90 code give the same results for the Jacobian-vector product J(z0) z for some randomly chosen vectors z0, z? -- Pauli Virtanen _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
