[petsc-users] PetscLayout and GetRange

[Weston Lowrie]

I don't think there is a inefficiency here.  It will be just one extra
empty vector since all the other "real" ones are identical size.  Sounds
like a good strategy to me.

I'm not quite at the stage where I can profile yet.  I will send if I can
get it to a point where it might be significant.

Thanks for the help,
Wes



On Tue, Jan 15, 2013 at 5:26 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 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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