| 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: Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>
- Date: Wed, 25 Aug 2010 17:16:17 +0200
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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 ?
Bastien