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

[neil liu]

I think I understood that.

1) In order to save memory, use a larger real system
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.

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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