Re: [ublas] unsubscribe

Subject: Re: [ublas] unsubscribe
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-05-20 02:24:03

Hi,

When multiplying a vector with a matrix from the right i.e. b=Ax (b,x 
vectors) as in the call in line 76
the result is defined as the scalar product of every row of the matrix 
with the vector. Which means that the result will have A.size1() 
entries.

When multiplying from the left as in b=xA it is the same as 
b=trans(A)x, so the result has A.size2() entries.

Hope i could help.

Greetings,
Oswin

On 2012-05-19 23:58, R Kannan wrote:
> On 4 May 2012 08:27, Hoerentrup Jobst
> <jobst.hoerentrup_at_[hidden] [5]> wrote:
>
>> Dear ublas experts,
>>
>> I am a newbie to ublas, but I have the impression there might be a
>> bug in axpy_prod:
>>
>> operation.hpp, line 76:
>>
>> Instead of
>>
>> Â  Â  Â  Â if (init)
>> Â  Â  Â  Â  Â  Â v.assign (zero_vector<value_type> (e1.size1 ()));
>>
>> I believe it should rather be
>>
>> Â  Â  Â  Â if (init)
>> Â  Â  Â  Â  Â  Â v.assign (zero_vector<value_type> (e1.size2 ()));
>>
>> Reason: The length of the result vector should match the number
>> of matrix columns, not rows.
>>
>> Line 76 is just one example, there are a few more places
>> with the same potential bug.
>>
>> Ublas looks relatively mature to me, so am I missing something?
>>
>> Many thanks,
>>
>> Jobst
>>
>> ---
>>
>> Jobst Hörentrup
>> Technicolor R&I Germany
>>
>> jobst.hoerentrup_at_[hidden] [1]
>>
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>
>
>
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