[petsc-users] vector outer product

[Matthew Knepley]

On Thu, Aug 9, 2012 at 10:19 PM, Yifei Li <yifli82 at gmail.com> wrote:

>
>
> On Thu, Aug 9, 2012 at 10:59 PM, Matthew Knepley <knepley at gmail.com>wrote:
>
>> On Thu, Aug 9, 2012 at 9:56 PM, Yifei Li <yifli82 at gmail.com> wrote:
>>
>>> Matt,
>>>
>>> I'm new to PETSC, can you pls explain what you mean by 'keep it in
>>> unassembled form'?
>>>
>>
>> Just keep two vectors, u^T v, instead of the dense matrix.
>>
>>
> But I need the result of the outer product (e.g, A) for
> further calculation (e.g., A*W).
>

A * W = A * (u v^T) = (A * u) v^T

   Matt


>
>>
>>    Matt
>>
>>
>>> A small example would be nice too. Thanks
>>>
>>> Yifei
>>>
>>> On Thu, Aug 9, 2012 at 9:15 PM, Matthew Knepley <knepley at gmail.com>wrote:
>>>
>>>> On Thu, Aug 9, 2012 at 5:39 PM, Yifei Li <yifli82 at gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I did not find any function doing this in the manual.  Could someone
>>>>> suggest a good way to do this?
>>>>>
>>>>
>>>> That gives a dense matrix. You would never want to do this. You would
>>>> keep it in unassembled form.
>>>>
>>>>     Matt
>>>>
>>>>
>>>>>
>>>>> Thanks
>>>>>
>>>>> Yifei
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>>
>>>
>>>
>>
>>
>> --
>> 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
>>
>
>


-- 
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
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