On Mon, Dec 5, 2016 at 1:32 PM, Emil Constantinescu <[email protected]> wrote:
> This was introduced to allow for full flexibility in ARKIMEX: i.e., use > IMEX or just the implicit part. It makes a difference whether the equation > is implicit F(u,u_dot) = 0 (possibly a DAE), or just u_dot=f(u). The former > has more restrictions and the algorithm is a bit more costly and > complicated. > > TS_EQ_UNSPECIFIED reverts to the original use of ARKIMEX: u_dot = f(u) + > g(u). > > Additional types are introduced for future use. This is not a useful answer since it gives us no idea how to procede. Its more like an encyclopedia entry. Matt > > Emil > > > On 12/5/16 10:26 AM, Brad Aagaard wrote: > >> Matt and the rest of the PETSc developers, >> >> This issue is not whether the TS is linear or nonlinear, but whether it >> is explicit or implicit. As far as I can tell only TS type >> Implicit-Explicit Runge Kutta makes use of the equation_type. >> >> The equations types defined in petscts.h are: >> >> TS_EQ_UNSPECIFIED = -1, >> TS_EQ_EXPLICIT = 0, >> TS_EQ_ODE_EXPLICIT = 1, >> TS_EQ_DAE_SEMI_EXPLICIT_INDEX1 = 100, >> TS_EQ_DAE_SEMI_EXPLICIT_INDEX2 = 200, >> TS_EQ_DAE_SEMI_EXPLICIT_INDEX3 = 300, >> TS_EQ_DAE_SEMI_EXPLICIT_INDEXHI = 500, >> TS_EQ_IMPLICIT = 1000, >> TS_EQ_ODE_IMPLICIT = 1001, >> TS_EQ_DAE_IMPLICIT_INDEX1 = 1100, >> TS_EQ_DAE_IMPLICIT_INDEX2 = 1200, >> TS_EQ_DAE_IMPLICIT_INDEX3 = 1300, >> TS_EQ_DAE_IMPLICIT_INDEXHI = 1500 >> >> For PyLith we would like the TS implementation (type) to set the >> equation type so we can detect whether the user has specified an >> implicit or explicit algorithm and set the residual and Jacobian >> functions appropriately. For example, the user may want to solve the >> linear elasticity equation for a quasi-static problem with implicit time >> stepping or a dynamic problem with explicit time stepping. >> >> Brad >> >> On 12/03/2016 12:20 PM, Matthew Knepley wrote: >> >>> On Sat, Dec 3, 2016 at 2:18 PM, Barry Smith <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>> > On Dec 3, 2016, at 11:58 AM, Matthew Knepley <[email protected] >>> <mailto:[email protected]>> wrote: >>> > >>> > Right now, TS just leaves the equation type as undetermined, and >>> never queries it except for the IMEX methods. This seems really >>> strange to me. If we choose a linear TS solver, shouldn't it set the >>> type to LINEAR, and likewise for nonlinear? Then a user could query >>> this for information. We want to do just that in PyLith. >>> >>> Is your concern that many of the examples never bother to set the >>> type? >>> >>> >>> Yes, since I want to query this to see what formulation the user expects. >>> >>> >>> Or that not enough error checking is done that the set type works >>> with solution method selected by the user? >>> >>> >>> No >>> >>> >>> I think these are just oversights and you should go ahead and add >>> these in the examples and code where appropriate. >>> >>> >>> Will do. >>> >>> Matt >>> >>> >>> >>> Barry >>> >>> > >>> > Matt >>> > >>> > -- >>> > What most experimenters take for granted before they begin their >>> experiments is infinitely more interesting than any results to which >>> their experiments lead. >>> > -- Norbert Wiener >>> >>> >>> >>> >>> -- >>> What most experimenters take for granted before they begin their >>> experiments is infinitely more interesting than any results to which >>> their experiments lead. >>> -- Norbert Wiener >>> >> >> -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
