Thanks, I now understand the situation. I have a tentative solution for you that does not require complex new APIs. I have added one function to the master branch MatSNESMFGetSNES() and attach a modified example that utilizes this to avoid the extra function evaluations.
Please let me know if it works for you and what you think,
Barry
> On Jan 26, 2018, at 5:54 PM, Alexander Lindsay <alexlindsay...@gmail.com>
> wrote:
>
> We are doing something non-standard. We set different functions for snes and
> mffd. When a function is called through snes, we know we are doing a
> non-linear residual evaluation and we allow an update of our mechanical
> contact nodes. When a function is called through mffd, we know we are within
> the linear solve, and we do not allow our contact state to change. If after a
> contact update our non-linear residual is not deemed to be converged, then we
> would hope to be able to re-use it for the zeroth-linear residual.
>
> I know that you don't like this way of handling contact, but it integrates
> well for us into our multiphysics framework and works well in many cases.
>
> On Jan 26, 2018, at 5:34 PM, Kong, Fande <fande.k...@inl.gov> wrote:
>
>> Hi Barry,
>>
>> I made minor changes on src/snes/examples/tutorials/ex2.c to demonstrate
>> this issue. Please see the attachment.
>>
>> ./ex2 -snes_monitor -ksp_monitor -snes_mf_operator 1
>>
>>
>> atol=1e-50, rtol=1e-08, stol=1e-08, maxit=50, maxf=10000
>> FormFunction is called
>> 0 SNES Function norm 5.414682427127e+00
>> 0 KSP Residual norm 9.559082033938e-01
>> FormFunction is called
>> FormFunction is called
>> 1 KSP Residual norm 1.703870633386e-09
>> FormFunction is called
>> FormFunction is called
>> 1 SNES Function norm 2.952582481151e-01
>> 0 KSP Residual norm 2.672054855433e-02
>> FormFunction is called
>> FormFunction is called
>> 1 KSP Residual norm 1.519298012177e-10
>> FormFunction is called
>> FormFunction is called
>> 2 SNES Function norm 4.502289047587e-04
>> 0 KSP Residual norm 4.722075651268e-05
>> FormFunction is called
>> FormFunction is called
>> 1 KSP Residual norm 3.834927363659e-14
>> FormFunction is called
>> FormFunction is called
>> 3 SNES Function norm 1.390073376131e-09
>> number of SNES iterations = 3
>>
>> Norm of error 1.49795e-10, Iterations 3
>>
>> "FormFunction" is called TWICE at "0 KSP".
>>
>> If we comment out MatMFFDSetFunction:
>>
>> /* ierr =
>> MatMFFDSetFunction(Jacobian,FormFunction_MFFD,(void*)snes);CHKERRQ(ierr); */
>>
>>
>> ./ex2 -snes_monitor -ksp_monitor -snes_mf_operator 1
>>
>> atol=1e-50, rtol=1e-08, stol=1e-08, maxit=50, maxf=10000
>> FormFunction is called
>> 0 SNES Function norm 5.414682427127e+00
>> 0 KSP Residual norm 9.559082033938e-01
>> FormFunction is called
>> 1 KSP Residual norm 1.703870633386e-09
>> FormFunction is called
>> FormFunction is called
>> 1 SNES Function norm 2.952582481151e-01
>> 0 KSP Residual norm 2.672054855433e-02
>> FormFunction is called
>> 1 KSP Residual norm 1.519298012177e-10
>> FormFunction is called
>> FormFunction is called
>> 2 SNES Function norm 4.502289047587e-04
>> 0 KSP Residual norm 4.722075651268e-05
>> FormFunction is called
>> 1 KSP Residual norm 3.834927363659e-14
>> FormFunction is called
>> FormFunction is called
>> 3 SNES Function norm 1.390073376131e-09
>> number of SNES iterations = 3
>>
>> Norm of error 1.49795e-10, Iterations 3
>>
>> "FormFunction" is called ONCE at "0 KSP".
>>
>> Hopefully, this example makes the point clear.
>>
>>
>> Fande,
>>
>> On Fri, Jan 26, 2018 at 3:50 PM, Smith, Barry F. <bsm...@mcs.anl.gov> wrote:
>>
>>
>> So you are doing something non-standard? Are you not just using -snes_mf
>> or -snes_mf_operator? Can you send me a sample code that has the extra
>> function evaluations? Because if you run through regular usage with the
>> debugger you will see there is no extra evaluation.
>>
>> Barry
>>
>>
>> > On Jan 26, 2018, at 4:32 PM, Kong, Fande <fande.k...@inl.gov> wrote:
>> >
>> >
>> >
>> > On Fri, Jan 26, 2018 at 3:10 PM, Smith, Barry F. <bsm...@mcs.anl.gov>
>> > wrote:
>> >
>> >
>> > > On Jan 26, 2018, at 2:15 PM, Kong, Fande <fande.k...@inl.gov> wrote:
>> > >
>> > >
>> > >
>> > > On Mon, Jan 8, 2018 at 2:15 PM, Smith, Barry F. <bsm...@mcs.anl.gov>
>> > > wrote:
>> > >
>> > >
>> > > > On Jan 8, 2018, at 2:59 PM, Alexander Lindsay
>> > > > <alexlindsay...@gmail.com> wrote:
>> > > >
>> > > > Is there any elegant way to tell whether SNESComputeFunction is being
>> > > > called under different conceptual contexts?
>> > > >
>> > > > E.g. non-linear residual evaluation vs. Jacobian formation from finite
>> > > > differencing vs. Jacobian-vector products from finite differencing?
>> > >
>> > > Under normal usage with the options database no.
>> > >
>> > > Hi Barry,
>> > >
>> > > How difficult to provide an API? Is it possible?
>> > >
>> > >
>> > >
>> > > If you have some reason to know you could write three functions and
>> > > provide them to SNESSetFunction(), MatMFFDSetFunction(), and
>> > > MatFDColoringSetFunction(). Note that these functions have slightly
>> > > different calling sequences but you can have all of them call the same
>> > > underlying common function if you are only interested in, for example,
>> > > how many times the function is used for each purpose.
>> > >
>> > > If we use this way for the Jacobian-free Newton, the function evaluation
>> > > will be called twice at the first linear iteration because the computed
>> > > residual vector at the nonlinear step is not reused. Any way to reuse
>> > > the function residual of the Newton step instead of recomputing a new
>> > > residual at the first linear iteration?
>> >
>> > It does reuse the function evaluation. Why do you think it does not? If
>> > you look at MatMult_MFFD() you will see the lines of code
>> >
>> > /* compute func(U) as base for differencing; only needed first time in
>> > and not when provided by user */
>> > if (ctx->ncurrenth == 1 && ctx->current_f_allocated) {
>> > ierr = (*ctx->func)(ctx->funcctx,U,F);CHKERRQ(ierr);
>> > }
>> >
>> > since the if is satisfied it does not compute the function at the base
>> > location. To double check I ran src/snes/examples/tutorials/ex19 with
>> > -snes_mf in the debugger and verified that the "extra" function
>> > evaluations are not done.
>> >
>> > In MatAssemblyEnd_SNESMF,
>> >
>> > if (j->func == (PetscErrorCode (*)(void*,Vec,Vec))SNESComputeFunction) {
>> > ierr = SNESGetFunction(snes,&f,NULL,NULL);CHKERRQ(ierr);
>> > ierr = MatMFFDSetBase_MFFD(J,u,f);CHKERRQ(ierr);
>> > } else {
>> > /* f value known by SNES is not correct for other differencing
>> > function */
>> > ierr = MatMFFDSetBase_MFFD(J,u,NULL);CHKERRQ(ierr);
>> > }
>> >
>> >
>> > Will hit ierr = MatMFFDSetBase_MFFD(J,u,NULL);CHKERRQ(ierr), because SNES
>> > and MAT have different function pointers.
>> >
>> > In MatMFFDSetBase_MFFD(Mat J,Vec U,Vec F),
>> >
>> > if (F) {
>> > if (ctx->current_f_allocated) {ierr =
>> > VecDestroy(&ctx->current_f);CHKERRQ(ierr);}
>> > ctx->current_f = F;
>> > ctx->current_f_allocated = PETSC_FALSE;
>> > } else if (!ctx->current_f_allocated) {
>> > ierr = MatCreateVecs(J,NULL,&ctx->current_f);CHKERRQ(ierr);
>> >
>> > ctx->current_f_allocated = PETSC_TRUE;
>> > }
>> >
>> > Because F=NULL, we then have ctx->current_f_allocated = PETSC_TRUE.
>> >
>> > Then, the following if statement is true:
>> >
>> > if (ctx->ncurrenth == 1 && ctx->current_f_allocated) {
>> > ierr = (*ctx->func)(ctx->funcctx,U,F);CHKERRQ(ierr);
>> > }
>> >
>> >
>> > Fande,
>> >
>> >
>> >
>> > Barry
>> >
>> >
>> > >
>> > > Fande,
>> > >
>> > >
>> > >
>> > > Barry
>> > >
>> > >
>> > >
>> > > >
>> > > > Alex
>> > >
>> > >
>>
>>
>> <ex2.c>
ex3.c
Description: ex3.c
