Seems those last few significant figures were significant after all. Now to figure out why getting rid of them gets a better answer than leaving them in...
Thanks for the help, I'll root around a bit more. On 9 July 2014 09:41, Jed Brown <[email protected]> wrote: > Andrew Cramer <[email protected]> writes: > > > I get *significantly *different results from backslash and petsc using > > the *same > > matrix*. > > > > Deflection |Au-b|/|b| > > Euler-Bernoulli: 4000 > > Petsc: 4386 0.3 > > Matlab: 4013 1.6e-10 > > > > I'm exporting to 6 significant figures. Condition number is rather poor > > (~2e7) but I get similar or worse results with problems having lower > > conditions numbers (~1e3). > > Are you sure the matrices are the same? Use "-ksp_view_mat binary", > then in MATLAB, A = PetscBinaryRead('binaryoutput') if you want to get > both matrices in the same environment. Or explicitly compute the norms > in PETSc. > > To debug, start with the simplest and most well-conditioned problem > that exhibits the issue. >
