Re: [Boost-users] Multiplying a matrix and vector ===> vector

Subject: Re: [Boost-users] Multiplying a matrix and vector ===> vector
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-10-26 13:49:44

Have you tried:

vector z = prod(m,x);

On 2012-10-26 13:08, Vipin Varma wrote:
> Dear all,
>
> My basic requirement is to multiply a matrix and a vector and then to
> store it into a vector using Boost's UBLAS.
>
> When I multiply a boost::numeric::ublas::compressed_matrix with a
> boost::numeric::ublas::vector using prod(matrix, vector), the output
> is a boost::numeric::ublas::matrix_vector_binary1. E.g.
> <PSEUDOCODE>
> boost::numeric::ublas::compressed_matrix m;
> boost::numeric::ublas::vector x;
> boost::numeric::ublas::matrix_vector_binary1<compressed_matrix, 
> vector, ?
>> tmp;
> tmp = prod(m,x);
> <PSEUDOCODE>
> The problem is that in the third field --- which expects the
> operation type --- in line 3, I do not know what to enter or how to
> specify the type of operation; I tried '*' and 'prod' and 'vector' 
> and
> 'compressed_matrix' but none work.
>
> Alternatively, I can avoid the tmp variable altogether and get a
> working program to copy the result of matrix-vector multiplication
> onto a new vector y but then I would need two multiplications. E.g.
> <CODE>
> std::copy(prod(m,x).begin(), prod(m,x).end(), y.begin());
> <CODE>
>
> Any suggestions on how to declare a matrix_vector_binary1 correctly
> or how to get the finaly result efficiently onto a vector will be
> appreciated.
>
> Regards,
> Vipin
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