I stuck the line

  PetscOptionsSetValue(NULL,"-snes_qn_m", "50");

in src/snes/examples/tutorials/ex19.c 

and called it with 

-da_refine 2 -snes_monitor -snes_type qn -snes_view

and the results showed

Stored subspace size: 50

so I am afraid it is something unique to exactly your code that is causing it 
to be not used. If you can send us a complete code that reproduces the problem 
we can track it down and fix it but without a reproducing code we can't do 
anything to resolve the problem.

   Barry


> On Feb 14, 2018, at 9:15 PM, Bikash Kanungo <bik...@umich.edu> wrote:
> 
> Thanks Barry and Matthew.
> 
> @Barry: I'm following the same procedure as you've mentioned - 
> PetscOptionsSetValue() precede SNESSetFromOptions. Here's the snippet for my 
> code:
> 
> -----------------------------------------------------------------------------------------------------------
> 
>       error = SNESCreate(PETSC_COMM_WORLD,&snes);
>       checkPETScError(error,
>                 "SNESCreate failed.");
>       
>       error = SNESSetType(snes, SNESQN);
>       checkPETScError(error,
>                 "SNESSetType failed.");
>       
>       error = SNESQNSetType(snes, SNES_QN_LBFGS);
>       checkPETScError(error,
>                 "SNESQNSetType failed.");
>       
>       error = SNESQNSetScaleType(snes, SNES_QN_SCALE_SHANNO);
>       checkPETScError(error,
>                 "SNESQNSetScaleType failed.");
>       
>       error = SNESQNSetRestartType(snes, SNES_QN_RESTART_PERIODIC);
>       checkPETScError(error,
>                 "SNESQNSetRestartType failed.");
>       
>       error = PetscOptionsSetValue("-snes_qn_m","500");
>       checkPETScError(error,
>                 "PETScOptionsSetValue failed.");
> 
>       SNESLineSearch linesearch;
>       error = SNESGetLineSearch(snes,&linesearch);
>       checkPETScError(error,
>                 "SNESGetLineSearch failed.");
>     
>       error = SNESLineSearchSetType(linesearch,SNESLINESEARCHCP);
>       checkPETScError(error,
>                 "SNESLineSearchSetType failed.");
>       
>       error = PetscOptionsSetValue("-snes_linesearch_max_it", "1");
>       checkPETScError(error,
>                 "PetscOptionsSetValue failed.");
> 
>       error = SNESLineSearchView(linesearch, PETSC_VIEWER_STDOUT_WORLD);
>       checkPETScError(error,
>                 "SNESLineSearchView failed.");
> 
>       error =SNESLineSearchSetMonitor(linesearch, 
>                                       PETSC_TRUE);
>       checkPETScError(error,
>                 "SNESLineSearchSet Monitor failed.");
> 
>       error = SNESLineSearchSetFromOptions(linesearch);
>       checkPETScError(error,
>                 "SNESLineSearchSetFromOptions failed.");
> 
>       SNESLineSearchReason lineSearchReason;
>       error = SNESLineSearchGetReason(linesearch, &lineSearchReason);
>       checkPETScError(error,
>                 "SNESLineSearchGetReason failed.");
> 
>       error = SNESSetFunction(snes,r,FormFunction,&petscData);
>       checkPETScError(error,
>                 "SNESSetFunction failed.");
>       
>       //
>       // Customize KSP 
>       //
>       error = SNESGetKSP(snes,&ksp);
>       checkPETScError(error,
>                 "SNESGetKSP failed.");
>       
>       error = KSPSetType(ksp,KSPGMRES);
>       checkPETScError(error,
>                 "KSPSetType failed.");
>       
>       error = KSPGMRESSetRestart(ksp,300);
>       checkPETScError(error,
>                 "KSPGMRESSetRestart failed.");
>       
>       error = KSPSetInitialGuessNonzero(ksp,PETSC_TRUE);
>       checkPETScError(error,
>                 "KSPSetInitialGuessNonzero failed.");
>       
>       error = KSPGetPC(ksp,&pc);
>       checkPETScError(error,
>                 "KSPGetPC failed.");
>       
>       error = PCSetType(pc,PCJACOBI);         
>       checkPETScError(error,
>                 "PCSetType failed.");
>       
>       error = PCSetReusePreconditioner(pc,PETSC_TRUE);
>       checkPETScError(error,
>                 "PCSetReusePreconditioner failed.");
>      
>       error = KSPSetTolerances(ksp,
>                 PETSC_DEFAULT,
>                 1e-15,
>                 1e7,
>                 10000); 
>       checkPETScError(error,
>                 "KSPSetTolerances failed.");
> 
>       error = KSPSetFromOptions(ksp);
>       checkPETScError(error,
>                 "Call to KSPSetFromOptions() failed.");
>         
>       //
>       //get reason for non-convergence
>       //
>       KSPConvergedReason kspReason;
>       error = KSPGetConvergedReason(ksp, &kspReason);
>       checkPETScError(error,
>                 "Call to KSPGetConvergedReason() failed.");
> 
>       if(kspReason < 0)
>       {
>           if(debugLevel != 0)
>           std::cout<<"Other kind of divergence in SNES-KSP : "<< kspReason 
> <<std::endl;
>         
>       } 
> 
>       PetscInt lag = 1;
>       error = SNESSetLagPreconditioner(snes,
>                        lag);
>       checkPETScError(error,
>                 "Call to SNESSetLagPreconditioner() failed.");
>       
>       PetscInt maxFails = 2;
>       error = SNESSetMaxLinearSolveFailures(snes,maxFails);
>       checkPETScError(error,
>                 "Call to SNESSetMaxLinearSolveFailures() failed.");
>       
>       PetscReal abstol = 1e-13; // absolute convergence tolerance
>       PetscInt  maxit  = 100000;
>       error = SNESSetTolerances(snes,
>                 abstol,
>                 PETSC_DEFAULT,
>                 PETSC_DEFAULT,
>                 maxit,
>                 maxit);
>       checkPETScError(error,
>                 "SNESSetTolerances failed.");
>       
>       error = SNESView(snes,
>                 PETSC_VIEWER_STDOUT_WORLD);
>       checkPETScError(error,
>                 "Call to SNESView() failed.");
> 
>       error = SNESMonitorSet(snes,SNESMonitorDefault,PETSC_NULL,PETSC_NULL);
>       checkPETScError(error,
>                 "Call to SNESMonitorSet() failed.");
> 
>       error = SNESSetFromOptions(snes);
>       checkPETScError(error,
>                 "Call to SNESSetFromOptions() failed.");
> 
> 
>       //
>       // Solve the system
>       //
>       error = SNESSolve(snes,PETSC_NULL,x);
>       checkPETScError(error,
>                 "Call to SNESSolve() failed.");
> 
>       SNESConvergedReason reason;
>       error = SNESGetConvergedReason(snes,&reason);
>       checkPETScError(error,
>                 "Call to SNESGetConvergedReason() failed.");
> 
> ------------------------------------------------------------------------------------------------------------------------------------
> 
> Also, I didn't find any SNESQN examples in my snes/examples folder (using 
> petsc-3.6.3). 
> Moreover, the Powell descent condition seems to be only declared and then 
> assigned a value through the PetscOptionsReal call. Beyond that I didn't find 
> any other mention of it. I was grepping for powell_downhill variable. (Note: 
> powell_downhill features in 3.6.3 and not in 3.7 version). 
> 
> Thanks,
> Bikash
> 
> 
> On Wed, Feb 14, 2018 at 7:02 PM, Matthew Knepley <knep...@gmail.com> wrote:
> On Wed, Feb 14, 2018 at 6:43 PM, Smith, Barry F. <bsm...@mcs.anl.gov> wrote:
> 
>   Hmm,
> 
> 1) make sure you call PetscOptionsSetValue() before you call to 
> SNESSetFromOptions()
> 
> 2) make sure you call SNESSetFromOptions()
> 
> 3) did you add a prefix to the SNES object? If so make sure you include it in 
> the PetscOptionsSetValue() call.
> 
>   I can't see a reason why it won't work. Does it work with the PETSc 
> examples for you or not?
> 
>    Regarding the Powell descent option, I'm afraid you'll need to examine the 
> code for exact details. src/snes/impls/qn/qn.c
> 
> Here is the description
> 
>   
> https://bitbucket.org/petsc/petsc/src/939b553f045c5ba32242d0d49e80e4934ed3bf76/src/snes/impls/qn/qn.c?at=master&fileviewer=file-view-default#qn.c-451
> 
>    Thanks,
> 
>      Matt
>  
> 
>   Barry
> 
> 
> > On Feb 14, 2018, at 5:25 PM, Bikash Kanungo <bik...@umich.edu> wrote:
> >
> > Hi,
> >
> > I'm using the L-BFGS QN solver. In order to set the number of past states 
> > (also the restart size if I use Periodic restart), to say 50, I'm using 
> > PetscOptionsSetValue("-snes_qn_m", "50"). However while running, it still 
> > shows "Stored subspace size: 10", i.e., the default value of 10 is not 
> > overwritten.
> >
> > Additionally, I would like to know more about the the 
> > -snes_qn_powell_descent option. For Powell restart, one uses a gamma 
> > parameter which I believe is defined by the -snes_qn_powell_gamma option. 
> > What exactly does the descent condition do? It would be useful if there are 
> > good references to it.
> >
> > Thanks,
> > Biksah
> >
> > --
> > Bikash S. Kanungo
> > PhD Student
> > Computational Materials Physics Group
> > Mechanical Engineering
> > University of Michigan
> >
> 
> 
> 
> 
> -- 
> 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
> 
> https://www.cse.buffalo.edu/~knepley/
> 
> 
> 
> -- 
> Bikash S. Kanungo
> PhD Student
> Computational Materials Physics Group
> Mechanical Engineering 
> University of Michigan


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