Re: [eigen] How to squeeze in place a vector matrix

[Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>]

On Wed, Aug 25, 2010 at 5:21 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> 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().

Thanks

And i will welcome a punchout(row i, colum i) method for the next api
revision :)

Bastien