> On Jul 24, 2017, at 5:03 AM, Stefano Zampini <[email protected]> > wrote: > > > > 2017-07-24 11:26 GMT+03:00 Lisandro Dalcin <[email protected]>: > On 23 July 2017 at 21:42, Barry Smith <[email protected]> wrote: > > > > Then explicit methods could automatically use a solve to apply the mass > > matrix inverse for each "right hand side" application and implicit methods > > could automatically "drop in" the mass matrix with the shift when a right > > hand side Jacobian is given also. Instead of requiring the user to handle > > this themselves. Are there any gotcha's that I am missing or is this > > relatively straightforward? > > > > > IMHO I think that it is not worth the complication. I value the generality of > the current API, that already is somewhat cumbersome to maintain. > Users providing the RHS function + mass matrix already know that they should > do M^-1 * rhsvec to compute the rhs function.
Then they get wrong or confusing information with TSAdjoint, not a good thing. > Same for the RHS jacobian. > > > > > Why wouldn't we have this interface? > > > > > What if the user provides MassMatrix + IFunction/IJacobian + > RHSFunction/RHSJacobian? Are you going to handle all the possible scenarios? > Error? dump a warning with PetscInfo? Users that will need such a new API > usually don't read PetscInfo output Error > > > As usual, the problem is on defining the interface and the trade on > performance and generality. But I'm definitely +1 on this. > > > Almost for sure MFEM must have this type of API. > > > > > No. AFAIK, sundials has it, not MFEM. > Natively in MFEM, they just suppors explicit Sure but this can still be an explicit method (though it has a solve in it). But I thought they were solving mass matrix systems all over the place? One of the CEED benchmarks is solving a mass matrix system. > or SDIRK. They also have interface to TS and Sundials. > > See https://github.com/mfem/mfem/blob/master/examples/ex9.cpp#L329 for native > explicit ode solvers in MFEM. > See here for the virtual method that allows using SDIRK > https://github.com/mfem/mfem/blob/master/examples/ex10.cpp#L91 > Here for sundials https://github.com/mfem/mfem/tree/master/examples/sundials > > With that said, if you want to use TS through MFEM, here you have an example > https://github.com/mfem/mfem/blob/master/examples/petsc/ex9p.cpp, which is > meant to be illustrative of the capabilities of the IFunction/RHSFunction > (and jacobians) API in PETSc, not efficiency. > > > Stefano will love it for sure... > > > -- > Lisandro Dalcin > ============ > Research Scientist > Computer, Electrical and Mathematical Sciences & Engineering (CEMSE) > Extreme Computing Research Center (ECRC) > King Abdullah University of Science and Technology (KAUST) > http://ecrc.kaust.edu.sa/ > > 4700 King Abdullah University of Science and Technology > al-Khawarizmi Bldg (Bldg 1), Office # 0109 > Thuwal 23955-6900, Kingdom of Saudi Arabia > http://www.kaust.edu.sa > > Office Phone: +966 12 808-0459 > > > > -- > Stefano
