[petsc-users] Solving Poisson equation with multigrid

[Jed Brown]

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Michele Rosso <mrosso at uci.edu> writes:

> If you are referring to -pc_type gamg, I tried it, but I got the same 
> error message
> (For coloring efficiency ensure number of grid points in X is divisible 
> by 2*stencil_width + 1)

The option could not have been used.  Always send the ENTIRE error
message.  Is the code calling KSPSetFromOptions()?  Run with
-options_left to see if any options did not get used.

> On 05/17/2013 04:49 PM, Jed Brown wrote:
>>
>> Read my first message
>>
>> On May 17, 2013 6:47 PM, "Michele Rosso" <mrosso at uci.edu 
>> <mailto:mrosso at uci.edu>> wrote:
>>
>>     Ok, I will give a try to AMG then. What is it exactly?
>>     Thank you!
>>
>>     On 05/17/2013 04:25 PM, Jed Brown wrote:
>>>     Michele Rosso<mrosso at uci.edu>  <mailto:mrosso at uci.edu>  writes:
>>>
>>>>     So should I always use an odd number of grid points?
>>>>     There is no way around this?
>>>     If you want to use regular geometric coarsening, then yes.  That *is*
>>>     regular node-centered coarsening.  Just consider the base case of one
>>>     element:
>>>
>>>
>>>        o ------- o
>>>
>>>     Split that in two:
>>>
>>>        o -- o -- o
>>>
>>>     Look, an odd number of vertices, and as we keep refining, it will stay
>>>     odd.
>>>
>>>     You can use AMG or write your own interpolation if you want irregular coarsening.
>>>
>>