[petsc-dev] TS Equation Type

[Emil Constantinescu]

On 12/5/16 3:28 PM, Matthew Knepley wrote:
> On Mon, Dec 5, 2016 at 1:32 PM, Emil Constantinescu
> <emconsta at mcs.anl.gov <mailto:emconsta at mcs.anl.gov>> 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.

I guess I don't understand the question. This setting is used only in 
-ts_type arkimex because it has implications to how the equation is 
interpreted -- see above; the user is not required to set it and we are 
not going to do so. This setting is not meant to be used as a selection 
tool. We rely on the user to use the appropriate solver. E.g., if the 
equation is implicit the user should not use explicit RK and so on...

Emil

>    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
>             <bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>
>             <mailto: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>
>             <mailto: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
>
>
>
>
>
> --
> 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