On 3/1/08, Charles R Harris <[EMAIL PROTECTED]> wrote: > So they differ in the least significant bit. Not surprising, I expect the > Fortran compiler might well perform operations in different order, > accumulate in different places, etc. It might also accumulate in higher > precision registers or round differently depending on hardware and various > flags.
Of course, but a completely unrelated but equivalent C implementation of this problem, as you can check in line 313 at this link http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/src/snes/examples/tutorials/ex5.c.html behaves almost the same that my F90 implemented residual. Perhaps Fortran compiler (gfortran) will generate the same code as the C one, but I'm not sure, Fortran compilers can be smarter that C compilers for this kind of looping. > The exp functions in Fortran and C might also return slightly > different results. I believe this is not the source of the problem, I've tried commenting that term, and differences are still there. > I don't think the differences are significant, but if you > really want to compare results you will need a higher precision solution to > compare against. I agree, the differences are not significant, but they end up having a noticeable impact. I'm still surprised!. Let's stop all this now. I'll be back as soon as I can produce some self-contained code to show and reproducing the problem. -- Lisandro Dalcín --------------- Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC - Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54-(0)342-451.1594 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
