[ublas] returning matrices/matrix_expressions

From: Nico Galoppo (nico_at_[hidden])
Date: 2006-02-22 11:09:42

Hi,

I've been wondering for a while now what the best way is to return 
matrices/matrix_expressions from functions, with the least copying possible. 
Until now, I've always gone the way of passing a matrix by reference, resizing 
that one to the required size and storing the result in there, like so:

template <typename matrix_type>
void f(matrix_type& m)
{
   m.resize(...);
   m.assign(...);
}

Unfortunately the syntax isn't always very clean, and sometimes I have to make 
temporaries anyways, before calling f(), like so:

...
   matrix_type a, b, tmp;
   f(tmp);
   noalias(a) = b + tmp;
...

Is there another way to go around this? Something like
template <typename E>
ublas::matrix_container<E> f()
{
   return ...
}

...
   noalias(a) = b + f();
...

I've looked around for programming guides on how to write your own functions 
that deal with ublas matrices, making use of ublas concepts such as template 
expressions; I've even followed some of the threads in the ublas mailing list, 
but it still is pretty much a mystery to me what goes on under the hood ;)

Thanks,

--nico

-- 
nico galoppo von borries     @  address: 105 creel st., chapel hill
comp. graphics phd. student  @           north carolina, 27516 USA
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                              @         [phone] (home)
                              @  email: nico at cs dot unc dot edu
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