Re: [ublas] Iterate over all elements of a matrix

From: Michele De Stefano (micdestefano_at_[hidden])
Date: 2007-08-26 05:11:27

Ok. I've looked at it. And where is the problem ? I think I've not fully
understood what do you want
to know.

One method of iteration through all the elements of a matrix is the one I
have explained before
(it is the more direct method, if you do not concern about the "scanning
order" of the elements).

The other method is the one shown into the example you suggested. In this
case, the author
uses the uBLAS iterators, that allow to you to selectively iterate along
columns (iterator1) and
along rows (iterator2). Furthermore, during the scanning, you can exchange
the kind of the
iterator you are using simply calling the begin() method of the iterator
itself. This method (and its
twin end() method) gives to you the starting iterator (or "past-the-end"
iterator, in the case of the
end() method) in the other direction, starting from the element into which
you are arrived. So, you
potentially can do a zig-zag path throug the matrix, if you continue to call
the begin() method to
switch the iterator you are using.

All this stuff is also explained into the official uBLAS documentation
(although I should admit that
the "double nature of an uBLAS iterator" is not sufficiently stressed).

On 8/25/07, Nuno Sucena Almeida <slug_at_[hidden]> wrote:
>
>
> Look at the Gunter Winkler sparse_io for example, you can use iterators:
>
> http://www.guwi17.de/ublas/examples/sparse_io.cpp
>
>                                         Nuno
>
> On Fri, Aug 24, 2007 at 07:17:13AM -0400, Neal Becker wrote:
> | Simple question.  How do I iterate over all elements of a matrix?
>
> --
> http://aeminium.org/slug
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