Hi Philippe, > What would you guys think about using some additional control over the > iterative solvers. I've thought about: > - Matrix-vector product policy : can be useful for "matrix-free" > implementations.
This already works. Just overload prod() and prod_impl() accordingly for a user 'matrix' type. I agree that an example should be added on how to do this, as this has shown up several times already: https://github.com/viennacl/viennacl-dev/issues/74 > - Custom stopping criterion Yes. At least provide a switch between 'true residual' and preconditioned residual. > - For CG, a policy for "what to do when the matrix is found to be > indefinite (pAp < 0) The easiest is to throw an exception. > I've had to reimplement CG for this reason (for nonlinear truncated > newton methods), and some others users might have had to reimplement > them too in some other context. 1.) It would be nice to provide a callback hook which gets called after each iteration with the current solution vector. This can be both a monitor and a custom stopping criterion at the same time. 2.) A status flag which indicates whether the function exited because of a successful termination, or whether the maximum number of iterations was reached, or the solver diverged. Possibly others. > Can you think about any other functors one could pass for other solvers > such as GMRES (for which I have no knowledge)? I can only think of very solver-specific quantities. For example, one can compute some estimates on the condition number from GMRES. What makes these changes somewhat messy is the current API: With x = solve(A, x, solver_tag()); the only possibility to provide these customizations is to put them into the tag, e.g. cg_tag my_cg_tag; my_cg_tag.set_something(a); x = solve(a, x, my_cg_tag()); assert( my_cg_tag.status() == VIENNACL_CG_CONVERGED ); which makes this all quite messy because the tag needs to be a const-reference, so all status flags and the like need to be mutable. This was a bad design choice... :-( I've got a couple of improvements to CG and friends in line, so I can also implement these extensions as needed. Any suggestions for further enhancements are welcome :-) Best regards, Karli ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ ViennaCL-devel mailing list ViennaCL-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viennacl-devel
