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.
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
