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

  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
> 

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