[petsc-users] why a certain option cannot be used

[Matthew Knepley]

On Wed, Jul 16, 2014 at 4:09 PM, Sun, Hui <hus003 at ucsd.edu> wrote:

>  I want to solve Stokes equation using user defined schur complement
> preconditioner. So I'm reading and testing snes/examples/tutorial/ex55.c,
> and ex70.c. In these examples, there are comments about the usage, for
> example:
>
>  mpiexec -n 2 ./stokes -nx 32 -ny 48 -fieldsplit_1_user_pc.
>
>  However the option -fieldsplit_1_user_pc is not recognized by the
> executable. The output of the above command is:
>

This ("user_pc") is just a mnemonic. What it means is that you can use any
PC in this slot. What he should have written is

  -fieldsplit_1_pc_type <user pc>

  Thanks,

     Matt


>   residual u = 2.6315e-05
>
>  residual p = 0.000229872
>
>  residual [u,p] = 0.000231373
>
>  discretization error u = 0.00633503
>
>  discretization error p = 0.121534
>
>  discretization error [u,p] = 0.121699
>
> WARNING! There are options you set that were not used!
>
> WARNING! could be spelling mistake, etc!
>
> Option left: name:-fieldsplit_1_user_pc (no value)
>
>
>  I'm wondering what's going on. Is that because I need some specific
> options during my configuring of the package? By the way, the version of
> PETSc I'm using is 3.4.4.
>
>
>  Best,
>
> Hui
>



-- 
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
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