[petsc-dev] TS Equation Type

[Brad Aagaard]

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 <bsmith at mcs.anl.gov
> <mailto:bsmith at mcs.anl.gov>> wrote:
>
>
>     > On Dec 3, 2016, at 11:58 AM, Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>> 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