[petsc-users] PetscLayout and GetRange

[Jed Brown]

On Tue, Jan 15, 2013 at 4:21 PM, Weston Lowrie <wlowrie at u.washington.edu>wrote:

> That's interesting.  If I understand you correctly, I would create a
> vector of the size I want specifically for calculating the ownership range,
> then use that on the real vectors.  Sounds like that would work.
>
> In my case, with many vectors, it does not make sense to copy them to a
> resized vector every time I want them to grow leading to many creates and
> destroys.
>

You can't dynamically resize vectors like that, and the global offsets
change when you resize.

Please profile before jumping to the conclusion that there is some terrible
inefficiency here. Unless all your loop does is create Vecs of different
sizes, chances are that the VecCreate is insignificant. If you have a
profile in which it's a big deal, please send the profile and explain what
you are doing and why.


>
> Wes
>
>
> On Tue, Jan 15, 2013 at 5:15 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> VecGetOwnershipRange()
>>
>> You can use VecCreateMPIWithArray() using your own array preallocated to
>> be as long as you want. If you profile, you'll probably find this is not a
>> meaningful optimization.
>>
>>
>> On Tue, Jan 15, 2013 at 4:12 PM, Weston Lowrie <wlowrie at uw.edu> wrote:
>>
>>> Hi,
>>>
>>> I have a problem where I want to grow the size of a Vec (or Mat) many
>>> times during program execution.  I think for efficiency purposes I would
>>> just want to allocate a maximum size, and then only use the portion that I
>>> need.  In the vector case, it is rather simple, just use the beginning of
>>> the vector, and add values to the end.
>>>
>>> This leads to me to the problem of processor ownership ranges.  From a
>>> previous email I noticed one could use the PetscLayout object and keep
>>> adjusting it as the useful part of the vector grows.  Does this sound like
>>> a good approach?
>>>
>>> I noticed the PetscLayout is not available in Fortran bindings.  Any
>>> workarounds for this?  I suppose I can just manually calculate the
>>> processor ranges?
>>>
>>> Thanks for the help,
>>> Wes
>>>
>>>
>>>
>>>
>>>
>>
>
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