[petsc-users] Inquiry about the PetscScalar in Petsc.

[neil liu]

Thanks for your explanation so much.

On Tue, Jul 11, 2023 at 12:41 PM Barry Smith <bsmith at petsc.dev> wrote:

>
>
> On Jul 11, 2023, at 12:16 PM, neil liu <liufield at gmail.com> wrote:
>
> I think I understood that.
>
> 1) In order to save memory, use a larger real system
>
>
>    This will save a little memory, but requires a slight change to your
> model/code for your problem
>
> 2) vec will store the real part with imaginary part equal to zero in the
> context of --scalar =complex. But this will not save memory.
>
>
>     This will waste a little memory.
>
>     Usually, coordinates do not take much of the total memory, that is
> solution vectors, matrices, intermediate work vectors for the solver take
> most of the memory
> so I suggest just using complex and not worrying about the few percent
> memory lost.
>
>
>
> Right?
>
> Thanks,
>
> Xiaodong
>
> On Tue, Jul 11, 2023 at 12:03 PM neil liu <liufield at gmail.com> wrote:
>
>> Do you mean that,
>>
>> even if I configure with --scalar=complex, when I use vecGetarray to get
>> the coords, the coords array is still stored in a real manner?
>>
>> Thanks,
>>
>> Xiaodong
>>
>> On Tue, Jul 11, 2023 at 11:54 AM Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Tue, Jul 11, 2023 at 11:48 AM neil liu <liufield at gmail.com> wrote:
>>>
>>>> Thanks for your reply.
>>>> I am using DMPLEX to read GMSH. And it seems I have to use
>>>> DMGetCoordinatesLocal();
>>>> VecGetArray(veccords, &coords);//it seems coords has to be defined by
>>>> complex either.
>>>>
>>>> 2) Store the coordinates in coords with imaginary part equal to zero.
>>>> I got the coordinates from above function *VecGetArray*, therefore
>>>> will this reduce the memory?
>>>>
>>>> 3) is a good way to work around that.
>>>>
>>>
>>> We just store them with real part 0.
>>>
>>>   Thanks,
>>>
>>>     Matt
>>>
>>>
>>>> On Tue, Jul 11, 2023 at 11:40 AM Barry Smith <bsmith at petsc.dev> wrote:
>>>>
>>>>>
>>>>>   Not really. PetscScalar (and entries of vectors etc) are either real
>>>>> or complex, they cannot be mixed.
>>>>>
>>>>>   What parts of PETSc are you using, DM?
>>>>>
>>>>>   You can
>>>>>
>>>>> 1) store the coordinates in arrays and not use Vec for them. (of if
>>>>> you are not using DM)
>>>>> 2) sore them in Vec but with imaginary part 0
>>>>> 3) rewrite your complex systems as real systems (with twice as many
>>>>> unknowns, but only real ones)
>>>>>
>>>>>   Barry
>>>>>
>>>>>
>>>>> > On Jul 11, 2023, at 11:34 AM, neil liu <liufield at gmail.com> wrote:
>>>>> >
>>>>> > Dear Petsc developers,
>>>>> >
>>>>> > My computation involves both real and complex numbers.
>>>>> > For example, my coordinate is real, but my matrix is complex.
>>>>> >
>>>>> > I use VecGetArray to get the coordinates. But it seems coordinates
>>>>> have to be defined in a complex manner to be consistent with complex
>>>>> matrix.
>>>>> >
>>>>> > Is there some ways to work around this if I understood correctly ?
>>>>> >
>>>>> > Thanks,
>>>>> >
>>>>> > Xiaodong
>>>>> >
>>>>> >
>>>>> >
>>>>>
>>>>>
>>>
>>> --
>>> 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
>>>
>>> https://www.cse.buffalo.edu/~knepley/
>>> <http://www.cse.buffalo.edu/~knepley/>
>>>
>>
>
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