[petsc-users] arkimex rejecting all dt in petsc 3.6.0

[Emil Constantinescu]

The results enclosed for 3.5.4 (354.txt) are not correct. I can tell 
that by looking at the first step. Most implicit schemes in arkimex have 
the first stage explicit and therefore need to be "started" somehow when 
dealing with algebraic constraints. In this case, a different scheme is 
used to start the integration.

Note that in 3.6 and 3.5.4_SEGV the first step uses scheme 1bee 
(scheme=0:'1bee') and then switches to '3'. This is the correct sequence 
otherwise inconsistent initial conditions are inadvertently used or the 
solver thinks it solves an ODE. I'm not sure why it's crashing in 
3.5.4_SEGV. Configuring with --with-debugging=yes may reveal more.

Emil

On 6/18/15 4:10 PM, Italo Tasso wrote:
> Thank you Barry and Emil.
>
> It works, but it takes twice as many steps than before.
>
> Was it wrong before? Should I have been using this option all along?
>
> I am solving the Navier-Stokes equations, full implicit and non-linear.
>
> I also noticed two things:
>
> In the 3.6.0 output, ts_monitor skips timestep #1.
>
> If I use the equation type in 3.5.4, I get segmentation fault.
>
> I attached the outputs.
>
>
>
>
>
> On Thu, Jun 18, 2015 at 1:24 PM, Emil Constantinescu
> <emconsta at mcs.anl.gov <mailto:emconsta at mcs.anl.gov>> wrote:
>
>     No, I'm not sure if it should. It belongs to the same category as
>     "problem_type" == TS_LINEAR / == TS_NONLINEAR.
>
>     Emil
>
>
>     On 6/18/15 11:15 AM, Abhyankar, Shrirang G. wrote:
>
>         Can the DAE equation type be supplied via a run-time option?
>
>         Shri
>
>         -----Original Message-----
>         From: barry smith <bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>>
>         Date: Thursday, June 18, 2015 at 11:08 AM
>         To: Italo Tasso <italo at tasso.com.br
>         <mailto:italo at tasso.com.br>>, "Constantinescu, Emil M."
>         <emconsta at mcs.anl.gov <mailto:emconsta at mcs.anl.gov>>
>         Cc: "petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>"
>         <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
>         Subject: Re: [petsc-users] arkimex rejecting all dt in petsc 3.6.0
>
>
>                Here is the response from Emil who made the changes to
>             the code
>
>             If you are solving a DAE then in the new version, we
>             introduced a new
>             flag that distinguishes between ODEs and DAEs leading to
>             different
>             semantics. For DAEs this is needed b/c it may not have
>             consistent initial
>             conditions.
>
>             If solving DAEs, the user has to set the EquationType
>             appropriately:
>             e.g.,
>             ierr =
>             TSSetEquationType(ts,TS_EQ_DAE_IMPLICIT_INDEX1);CHKERRQ(ierr);
>
>             This is documented in the doc, but I didn't add it to the
>             changelog (Jed
>             pointed it out to me).
>
>             Currently it only affects -ts_type arkimex. I'll work with
>             Satish to add
>             it to the changelog.
>
>             *If that's not the case:* let me know and we can dig deeper.
>
>             Emil
>
>                 On Jun 18, 2015, at 5:48 AM, Italo Tasso
>                 <italo at tasso.com.br <mailto:italo at tasso.com.br>> wrote:
>
>                 I just upgraded to 3.6.0 and my code stopped working.
>                 All dt are
>                 rejected. I used the same configure line, same code,
>                 same everything.
>
>                 With 3.5.4 I get:
>
>                 0 TS dt 1e-06 time 0
>                       0 SNES Function norm 2.549981005316e+05
>                       1 SNES Function norm 6.107056905987e-03
>                       2 SNES Function norm 1.483881932064e-10
>                       3 SNES Function norm 9.122873794272e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 3
>                       0 SNES Function norm 7.790429171165e+04
>                       1 SNES Function norm 7.289068747803e-04
>                       2 SNES Function norm 8.227639633330e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 2
>                       0 SNES Function norm 1.154356516184e+05
>                       1 SNES Function norm 2.309925413255e-03
>                       2 SNES Function norm 6.382141981406e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 2
>                         TSAdapt 'basic': step   0 accepted t=0
>                 + 1.000e-06
>                 wlte=0.000654 family='arkimex' scheme=0:'3' dt=1.000e-05
>
>                 With 3.6.0 I get:
>
>                 0 TS dt 1e-06 time 0
>                       0 SNES Function norm 2.549981005316e+05
>                       1 SNES Function norm 6.107056925316e-03
>                       2 SNES Function norm 1.519319591792e-10
>                       3 SNES Function norm 9.070104116945e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 3
>                       0 SNES Function norm 7.790429171165e+04
>                       1 SNES Function norm 6.942541792651e-04
>                       2 SNES Function norm 8.458781909516e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 2
>                       0 SNES Function norm 1.154356516184e+05
>                       1 SNES Function norm 2.287202942961e-03
>                       2 SNES Function norm 6.585201377573e-11
>                     Nonlinear solve converged due to CONVERGED_FNORM_ABS
>                 iterations 2
>                         TSAdapt 'basic': step   0 rejected t=0
>                 + 1.000e-06 wlte=
>                 324 family='arkimex' scheme=0:'3' dt=1.311e-07
>
>                 Any ideas? I attached the full output.
>
>                 Options I use:
>
>                 -ts_view -ts_type arkimex -ts_arkimex_fully_implicit
>                 -ts_adapt_monitor
>                 -ts_monitor -snes_monitor -snes_converged_reason
>                 -ksp_type preonly
>                 -pc_type lu -pc_factor_mat_solver_package mumps
>                 -snes_rtol 0 -snes_atol
>                 1e-10 -snes_stol 0
>
>                 <petsc354.txt><petsc360.txt>
>
>
>
>