Re: [eigen] Optimization for special complex operations

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

2010/8/16 Carlos Becker <carlosbecker@xxxxxxxxx>:
>
> On Mon, Aug 16, 2010 at 2:34 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
> wrote:
>>
>> 2010/8/16 Carlos Becker <carlosbecker@xxxxxxxxx>:
>> > Hi everyone again. Lately I've been using Eigen with complex numbers to
>> > calculate things such as calculating the maximum of the real part or
>> > imaginary part of a certain vector. I suppose that trying to take the
>> > real
>> > part and then use maxCoeff() or minCoeff() would create a possible
>> > unnecessary temporary.
>>
>> No, it wouldn't :-)
>
> Ok good, maybe 'temporary' is not exactly what I wanted to say. I mean that
> maybe there are vectorized ways to do certain stuff and special
> implementations could be provided for such operations.
>
>>
>> > Another thing is to be able to do something like:
>> >
>> > MatrixXf nn,xx;
>> > xx = nn.colwise().normalized();
>>
>> Hm. If we start going that route, won't we end up offering every
>> possible vector operation as colwise() operation?
>>
> .....
>>
>> The biggest reason not to do it now is that it really isn't necessary
>> to release Eigen 3.0 .... ;-)
>
>
> Yes I understand. I think vector-wise operations could be very important,
> but they would probably require a bit of discussion before implementing them
> (ie: should we keep .colwise(), should we use .vectorwise(), in the case
> some names for the reductions and vector-wise operations are the same). I
> believe these kind of operations would be very useful since many times a set
> of vectors is stored in a matrix, so this way the user could benefit from
> extra performance.

But the thing is, for this kind of use case, the much better approach
is to use a matrix-of-arrays:

Matrix<ArrayXf, 3, 1>

then all operations are automatically supported and vectorized.

The problem is that right now there is an inefficiency problem as we
create useless temporaries with Scalar=Array. This is the problem that
is the most worth fixing.

Benoit

> I could try some prototypes to see if I can make it work. I designing
> something like .vectorwise() could be fine.
> Carlos