On Thu, 22 Apr 2010 15:59:18 -0500, Barry Smith <bsmith at mcs.anl.gov> wrote: > > The petsc-maint request titled "Question on setting rtol in KSP" > points to a HUGE deficiency in PETSc.
I don't recieve petsc-maint, what was the request? > When PETSc returns an answer to a linear or nonlinear solver it > returns no useful information about how accurate that solution is. In > any other field beside numerical computing this would be considered > disgraceful. We should fix this for KSP and SNES and also make sure > that ALL the TS's allow proper error control (as some of them already > do?). So TS error *control* is quite hard and generally expensive, even for model problems. It's more common to attempt to keep *local* truncation error beneath a threshold and keep track of a posteriori estimates so that the results can be meaningfully assessed. A more reliable approach is adjoint-based error estimation. In any case, many popular integrators don't come with any cheap error estimates, so even just logging errors is not going to work for every TS implementation. I just wanted to point out that this is a huge field, and is intimately coupled with the spatial discretization, so I don't think it's feasible to provide goal-oriented (global) error control throughout TS. I do intend to provide discrete and continuous adjoints (assuming the user can provide an adjoint of the spatial discretization). Jed
