> On Aug 3, 2016, at 5:32 PM, Mark Adams <mfad...@lbl.gov> wrote: > > So if we are not using IMEX then the semantics of the TS are the same > if we put the terms (functions and Jacobians) on the LHS (F) or RHS > (G), with a sign change of course.
Yes. > And just to be 100% clear, if we put terms in the RHS (function) but > not in the G Jacobian, then this is like treating these terms with > forward Euler, is that right? Yes. If you only want to use an explicit method, you can just provide the RHS function without the RHS Jacobian. Hong > I that right? > > On Wed, Aug 3, 2016 at 3:01 PM, Hong Zhang <hongzh...@anl.gov> wrote: >> If you use a fully implicit method such as backward Euler, the G Jacobian >> will be used by PETSc. If you switch to an explicit method, the G Jacobian >> function will not be used. For IMEX, the G function is treated explicitly, >> so its Jacobian will not be used. >> >> Hong >> >>> On Aug 3, 2016, at 2:59 PM, Mark Adams <mfad...@lbl.gov> wrote: >>> >>> We have a question about the RHS Jacobian (G) for TS. The manual says: >>> >>> • Jacobian Gu >>> If using a fully implicit method and the function G() is provided, one >>> also can provide an appropriate (approximate) Jacobian matrix of G(). >>> >>> If we use, say, backward Euler and provide a G Jacobian, does PETSc >>> use this G Jacobian in some way? or is the G Jacobian only used for >>> IMEX methods? >>> >>> Mark >>