Re: [eigen] Vectorwise dot product feature request

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On 2010-07-07 15:40, Gael Guennebaud wrote:
actually, this is more subtle :) When an inner product is detected, it
returns an InnerProduct object which can be converted into a scalar

Interesting explanation, thanks.

I have another vectorwise question/request. I'd like to broadcast a coefficient-wise product like "mat.array().colwise() *= vec.array()". Is it possible to do this now? Or will it be in the future?

Kind regards,

On Wed, Jul 7, 2010 at 2:46 PM, Márton Danóczy<marton78@xxxxxxxxxx>  wrote:
Because .dot() returns a scalar, whereas multiplication returns an 1x1 matrix.


On 7 July 2010 14:15, Johan Pauwels<johan.pauwels@xxxxxxxxxxxxx>  wrote:
On 2010-07-07 13:02, Aron Ahmadia wrote:

That looks suspiciously like a transposed multiply to me...

Ugh, exactly. Sorry for the bother. My mind was so set on a collection of
independent columns and broadcasting operations, that I forgot the basic
matrix multiplication. One might wonder why there even is a .dot() syntax?



On Wed, Jul 7, 2010 at 1:59 PM, Johan Pauwels<johan.pauwels@xxxxxxxxxxxxx>
Hello all,

Would it be possible to allow a vectorwise dot product as in the example


int main()
    Eigen::MatrixXf mat = Eigen::MatrixXf::Random(5,2);
    Eigen::VectorXf vec = Eigen::VectorXf::Random(5);
    Eigen::RowVectorXf result(2);

    // this syntax
    result = mat.colwise().dot(vec);
    // instead of this for loop
    for (int i = 0; i<  mat.cols(); ++i)
        result[i] = mat.col(i).dot(vec);


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