Re: [boost] Re: ublas : size1 <-> nrows

From: Jeremy Siek (jsiek_at_[hidden])
Date: 2002-01-26 12:25:09

On Fri, 25 Jan 2002, jhrwalter wrote:
>
> Sure, we could eliminate x * A and force the user to always write
> (A^t * x^t)^t instead ;-). But if we would not, we could get code
> like the following for right and left multiplication with a vector:

I wasn't suggesting that you eliminate x * A. I was suggesting that you
/implement/ it by doing trans(trans(A) * trans(x)). In the MTL 3
prototype, the trans() function creates a transposed view wrapper. By
taking this implementation approach, you don't have to mess with multiple
the implementations of matrix-vector multiplication that you show below.
Also, the trans() wrappers are useful in their own right.

> Right multiplication:
>
> for (i = 0; i < A.range_size (); ++ i) {
>  r [i] = 0;
>  for (j = 0; j < A.domain_size (); ++ j)
>   r [i] += A [i] [j] * x [j];
> }
>
> Left multiplication:
>
> for (j = 0; j < A.domain_size (); ++ j) {
>  r [j] = 0;
>  for (i = 0; i < A.range_size (); ++ i)
>   r [j] += x [i] * A [i] [j];
> }
>

Cheers,
Jeremy

----------------------------------------------------------------------
 Jeremy Siek                          http://www.osl.iu.edu/~jsiek/
 Ph.D. Student, Indiana Univ. B'ton   email: jsiek_at_[hidden]
 C++ Booster (http://www.boost.org)   office phone: [phone]
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