[petsc-users] Neumann BC in src/ksp/ksp/example/tutorial/ex29.c

[Alan Wei]

Thanks, Matt. I thought there is a ghosted grid around Dirichlet and Neumann
BC's. ^_^

best,
Alan

On Fri, Sep 2, 2011 at 7:14 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Sep 1, 2011 at 9:47 PM, Alan Wei <zhenglun.wei at gmail.com> wrote:
>
>> Dear All,
>>     I hope you're having a nice day.
>>     I'm still working on this Poisson solver example, and I still have a
>> little confusion on the boundary condition. I wonder if I have a 17*17 grid.
>> (index i = 0~16 and j = 0~16, solving for variable 'u')
>> 1) If a Dirichlet BC applied on the left boundary, i.e. u= 1, is that all
>> values with u[i= 0][]  = 1 or with u[i= -1][]  = 1 (where, u[i=-1][] are
>> ghost grids left next to grid of u[i= 0][]).
>>
>
> Unless you define the boundary as PERIODIC or GHOSTED, the -1 does not
> exist. I set Dirichlet conditions at 0 and M-1.
>
>
>> 2) If a Neumann BC applied on the right boundary, i.e. du/dx = 0, is that
>> (u[i=16][]-u[i=15][])/dx= or  (u[i=17][]-u[i=16][])/dx = 0 (where u[i =17][]
>> are ghost grids right next to grid of u[i = 16][]).
>>    Thank you so much.
>>
>
> Same answer.
>
>     Matt
>
>
>> best,
>> Alan
>>
>>
>
>
> --
> 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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