On 2 Jul 2014, at 17:47, Miroslav Kuchta <[email protected]> wrote: > Hi, > > according to PETSc user manual [ch 4.6 Solving singular systems], nullspace > for > the Krylov Solver should be provided as an array of orthonormal vectors. I > think > it is then a good idea to make the constructor of VectorSpaceBasis check the > orthogonality. Or is the orthogonality property not necessary? >
The basis vectors should be orthogonal. Automated checking is not a good idea. It is a significant operation. It’s up to the user to check. Garth > I played with linear elasticity with no bcs on displacement, which is a > singular > problem and its solution requires eliminating the rigid motions. The basis > vectors > for rotation that I provided at first were describing rotation around origin > but that > was not center of gravity of my body. While these vectors were all in the > nullspace, > the basis was not orthogonal and I suspect that's why the solver would not > converge. > Once I shifted the domain, all was fine. So in my experience orthogonality is > crucial. > I'd be interested if somebody else has different/similar experience. Thanks. > > Regards, Miro > _______________________________________________ > fenics mailing list > [email protected] > http://fenicsproject.org/mailman/listinfo/fenics _______________________________________________ fenics mailing list [email protected] http://fenicsproject.org/mailman/listinfo/fenics
