Re: [eigen] Vectorwise dot product feature request

[Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>]

It is already possible. You can choose one of the following methods:

  mat.array() *=  Replicate<Vector2d,1,Dynamic>(vec,1,mat.cols()).array();
  mat.array() *=  vec.replicate(1,mat.cols()).array();

Here, they have probably the same performance.

- Hauke

On Wed, Jul 7, 2010 at 4:22 PM, Johan Pauwels
<johan.pauwels@xxxxxxxxxxxxx> wrote:
> 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
>> type:
>>
>
> 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,
> Johan
>>
>>
>> On Wed, Jul 7, 2010 at 2:46 PM, Márton Danóczy<marton78@xxxxxxxxx>  wrote:
>>
>>>
>>> Because .dot() returns a scalar, whereas multiplication returns an 1x1
>>> matrix.
>>>
>>> Marton
>>>
>>>
>>>
>>> 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?
>>>>
>>>> Regards,
>>>> Johan
>>>>
>>>> A
>>>>
>>>> On Wed, Jul 7, 2010 at 1:59 PM, Johan
>>>> Pauwels<johan.pauwels@xxxxxxxxxxxxx>
>>>> wrote:
>>>>
>>>>>
>>>>> Hello all,
>>>>>
>>>>> Would it be possible to allow a vectorwise dot product as in the
>>>>> example
>>>>> below?
>>>>>
>>>>> #include<Eigen/Core>
>>>>>
>>>>> 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);
>>>>>    }
>>>>> }
>>>>>
>>>>> Regards,
>>>>> Johan
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>
>
>
>