Re: [eigen] How to resize a partially fixed matrix

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2009/6/24 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
> On Wed, Jun 24, 2009 at 10:37 AM, Helmut
> Jarausch<jarausch@xxxxxxxxxxxxxxxxxxx> wrote:
>> Hi,
>>
>> I wonder how I can resize a matrix where one of the dimension is fixed,
>> like
>>
>> Matrix<double,4,Eigen::Dynamic> MS_BC;
>>
>> ....
>>
>> MS_BC.resize(5); //  this fails
>
> yes it fails because resize(int size) is for vector only.
>
>> but this works
>> MS_BC.resize(4,5);
>> but it's not logical?
>
> well that depends. First of all it is very clear that
> MS_BC.resize(4,5) *must* work. Now about allowing resize(int size) to
> work on such matrices why not. I guess that the main use case for such
> matrices is to use a Matrix to store a collection of small vectors,
> and so the matrix can be seen as a std::vector, and so having
> resize(int size) working makes sense. On the other hand, in that case
> the parameter "size" will mean either the number of rows or the number
> of cols depending on the context that is not very nice. So there are
> pro and cons, but eventually I'm 51% ok to extend resize to partially
> dynamic matrices.

Same here. It's the second time in a few days that people ask for
something like that, so i'd be OK to do this just to make our API
match what people expect. The "list of vectors" argument is good too.
And after all it doesn't look that dangerous.

But then we should do the same for other functions, for consistency:
- at least other Matrix methods like constructors, setZero...
- static MatrixBase methods like Zero...

more generally all methods that take size parameters!

> or, we add an explicit partial_resize(int size)
> function ?

hm not sure, since the main goal is to meet expectations of people who
expect resize(int) to work.

Benoit