[petsc-dev] TS Equation Type

[Matthew Knepley]

On Mon, Dec 5, 2016 at 1:32 PM, Emil Constantinescu <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.

   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>> 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
>>>
>>
>>


-- 
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
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