On 12/5/16 3:28 PM, Matthew Knepley wrote:
On Mon, Dec 5, 2016 at 1:32 PM, Emil Constantinescu
<[email protected] <mailto:[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.
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
<[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> wrote:
> On Dec 3, 2016, at 11:58 AM, Matthew Knepley
<[email protected] <mailto:[email protected]>
<mailto:[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
