| Re: [eigen] How to squeeze in place a vector matrix |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] How to squeeze in place a vector matrix
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Wed, 25 Aug 2010 11:21:54 -0400
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2010/8/25 Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>:
> On Wed, Aug 25, 2010 at 4:54 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>> 2010/8/25 Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>:
>>> On Wed, Aug 25, 2010 at 4:18 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>>>> 2010/8/25 Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>:
>>>>> Hi,
>>>>>
>>>>> I want to squeeze some line and column of matrix in place, in order to
>>>>> remove the null space.
>>>>>
>>>>> How can I do that?
>>>>>
>>>>> I have tryied block(i,j,k,l).eval() but i think it is suboptimal
>>>>
>>>> Ah, I see, trying to avoid aliasing issues.
>>>>
>>>> In fact, in assignments, we are always traversing matrices
>>>> left-to-right and top-to-bottom.
>>>>
>>>> So you can remove the eval() if you are a little careful. For example,
>>>> this works:
>>>>
>>>> matrix.block(i,j,k,l) = matrix.block(i+1,j,k,l); // squeeze row i
>>>>
>>>> Of course this is relying on undocumented behavior; but I really don't
>>>> see why we'd ever change this.
>>>
>>> Because it is really really useful removing null space on eigenvector
>>> decomposition** ?
>>
>> I wasn't questioning the interest of removing null parts of matrices :-)
>> I was saying that the behavior on why my trick above is relying,
>> though undocumented, is unlikely to change.
>>
>
> BTW this solution using block does not change the size of the matrix.
> Do you know how to change the size ?
Use conservativeResize().
Benoit
>
> Bastien
>
>
>