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

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

On Wed, Jun 24, 2009 at 6:06 PM, Markus Fröb<grey_earl@xxxxxx> wrote:
>> 24.06.09 17:55:10 "Benoit Jacob" <jacob.benoit.1@xxxxxxxxx>
>> 2009/6/24 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!
>>
>> I tried to do that change and now I think that it's very nontrivial:
>> not sure anymore that it's a good move!
>> Here's what makes me change my mind. Look at what happens when you do:
>>
>> Matrix<float,3,4> m;
>> m.resize(4);
>>
>> How to interprete this? Should this be a NOP or a failed assertion?
>> There are many such issues in Matrix.h alone and I am afraid that any
>> way to allow that will result in a much more complex Matrix.h and less
>> consistent API....
>>
>> Benoit
>
> I vote for a failed assertion here and still do the change otherwise.
> The single-argument resize already tests if it's a vector, no?
> So I think the change shouldn't be too big ...

same here.

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