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

Subject: Re: [Boost-users] Multiplying a matrix and vector ===> vector
From: Vipin Varma (varma_at_[hidden])
Date: 2012-10-27 07:10:38

Unfortunately I'm unable to get the below suggestion to work. Could you 
please mention if this was what you were referring to:
http://www.boost.org/doc/libs/1_49_0/libs/range/doc/html/range/reference/adaptors/introduction.html?

If so, the closest file I have in my Boost Version 1.0 is 
boost/range/iterator_range.hpp but 
that 
doesn't have the below copy function. I'll probably need to get the 1.49.0 
version then.

Thanks,
Vipin

On Sat, 27 Oct 2012, Nathan Ridge wrote:

>
>> 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>
>
> This doesn't answer your question, but I just wanted to point out that
> the above line is undefined behaviour, since the begin and end iterators
> refer to two different ranges (two different temporary variables). This
> problem can be avoided by using boost::copy (from Boost.Range) instead,
> which allows you to mention the range just once:
>
> boost::copy(prod(m, x), y.begin());
>
> Regards,
> Nate
>
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