[petsc-users] Non-uniform Cartisian Grid

[Matthew Knepley]

On Thu, Feb 28, 2013 at 7:19 PM, Zhenglun (Alan) Wei <zhenglun.wei at gmail.com
> wrote:

> Dear folks,
>     Here are several questions following up my previous ones:
> 1, I modified my code based on ex49.c. However, I found that if I don't
> call 'DMDASetUniformCoordinates' before calling 'DMDAVecGetArray', then an
> error comes up:
> [0]PETSC ERROR: Null argument, when expecting valid pointer!
> [0]PETSC ERROR: Null Object: Parameter # 2!
>     The code do works if I add a call for 'DMDASetUniformCoordinates' in
> it. However, I feel it is a waste of calling 'DMDASetUniformCoordinates'
> since what follows this calling is to change the coordinate to a
> non-uniform gird. Does it have any way to bypass this call or you think it
> is fine to keep it here.
>

If you do not call it, then you have to create the coordinate vector
yourself. I would just call it.


> 2, Also, if I do by this way, the outputted mesh looks weird, as shown in
> the figure.
>     I was trying to double the dy value manually in the
> SetNonUniformGrid(). However, the only mesh changed is just on the z=0 and
> x=0 plane. Here I attached my code. Do I need to do anything else except
> DMDAVecRestoreArray() after I modified the coordinate information?
>

I do not understand what you want here.

  Matt


> thanks,
> Alan
>
>
> On 2/26/2013 8:46 PM, Barry Smith wrote:
>
>> On Feb 26, 2013, at 4:49 PM, "Zhenglun (Alan) Wei"<zhenglun.wei at gmail.com>
>>  wrote:
>>
>>  Dear folks,
>>>       I have one question for the ex49.
>>>       It do show a way to 'get' the 'coord' by the 'DMDAVecGetArray'.
>>> Should I just modified the coordinate on the 'coord' in order to obtain a
>>> non-uniform grid? and then, use DMDAVecRestoreArray to link the modified
>>> 'coord' back to 'cda' so that the 'coord' will be updated to the mesh I
>>> want?
>>>
>>     Yes, you can do this.
>>
>>
>>  thanks,
>>> Alan
>>>
>>> On 2/22/2013 3:20 PM, Matthew Knepley wrote:
>>>
>>>> On Fri, Feb 22, 2013 at 3:57 PM, Zhenglun (Alan) Wei<
>>>> zhenglun.wei at gmail.com>  wrote:
>>>> Dear all,
>>>> I hope you're having a nice day.
>>>> I wonder if anyone could point out a example for me about the
>>>> DMDASetCoordinates(). I found this
>>>> (http://www.mcs.anl.gov/petsc/**petsc-current/src/dm/impls/da/**
>>>> dacorn.c.html#**DMDASetCoordinates<http://www.mcs.anl.gov/petsc/petsc-current/src/dm/impls/da/dacorn.c.html#DMDASetCoordinates>
>>>> )
>>>> online; however it does not really demonstrate how to create the
>>>> 'coordinate vector - c'.
>>>> Also, I found that in the petsc sub-folder:
>>>> /petsc-dev/src/dm/impls/patch has a patch.c, which I suppose that it
>>>> does a local refinement for mesh. Does this a mature model that we can
>>>> use or just a testing code?
>>>>
>>>> Look at KSP ex49. In the routine DMDACoordViewGnuplot2d() it reads out
>>>> the coordinates.
>>>> You could just as easily set them in this fashion.
>>>>
>>>>     Matt
>>>>   thanks,
>>>> Alan
>>>>
>>>> On 11/7/2012 6:55 PM, Barry Smith wrote:
>>>>
>>>>> On Nov 7, 2012, at 6:50 PM, Alan<zhenglun.wei at gmail.com>  wrote:
>>>>>
>>>>>  Dear folks,
>>>>>> I hope you're having a nice day.
>>>>>> I'm testing the Poisson solver in /src/ksp/ksp/examples/**
>>>>>> tutorials/ex45.
>>>>>> It uses the 'DMDACreate3d' to generate a Cartisian structured grid and
>>>>>> solve it with uniform grid size. However, I attempt to modify it to
>>>>>> obtain solution with a Cartsian structured grid and non-uniform grid
>>>>>> (It
>>>>>> is not unstructured local refined mesh). Should I still use the
>>>>>> 'DMDACreate3d' and implement different grid size in 'ComputeMatrix'
>>>>>> and
>>>>>> 'ComputeRHS'? In other words, does 'DMDACreate3d' itself include any
>>>>>> mesh size information?
>>>>>>
>>>>>     You can use DMDASetCoordinates() and DMDAGetCoordinates() (called
>>>>> DMSetCoordinates() and DMGetCoordinates() in petsc-dev) to keep track of
>>>>> the coordinates but you are responsible for generating the correctly scaled
>>>>> entries in the matrix etc.
>>>>>
>>>>>     Barry
>>>>>
>>>>>  thanks,
>>>>>> 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
>>>>
>>>
>


-- 
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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