Re: [ublas] find2 required by Matrix?

From: Shawn D. Pautz (sdpautz_at_[hidden])
Date: 2005-10-19 09:10:11

All,

It's my understanding that a generic programming concept specifies the 
minimum requirements for a class modeling that concept that clients 
(e.g. algorithms) may need.  The situation I described below seems to 
indicate that lu_factorize needs the find2 member function, either 
directly or through calls that it makes.  Am I correct in understanding 
then that the "M" template parameter of lu_factorize (i.e. the M 
concept) must provide find2?  Then either the Matrix concept must 
require find2, or M is a refinement of Matrix that makes additional 
requirements.

More generally, can we assume that the various ublas algorithms are 
designed to work with any containers modeling the Vector or Matrix 
concept?  It seems to me that this is the main reason to define those 
concepts in the first place.  I would like to use my own Vector and 
Matrix types in some situations, and it is far easier to make sure that 
these classes have the public interface specified by the documented 
concepts than to have to throw them at the various ublas algorithms to 
discover what they're missing.

In case this helps to understand my situation, my local classes are 
wrappers to bounded_vector and bounded_matrix ("has-a", not "is-a").  I 
want to provide only the minimum interface required by the Vector and 
Matrix concepts as a means of ensuring that I don't count on extra 
functionality, so that I can easily substitute the ublas containers 
directly at a later date.

As an aside, has anyone thought of defining similar minimal classes as a 
way to test the ublas algorithms (ignore efficiency and concentrate on 
the bare interface)?  I'm worried that there may have been some feature 
creep in both the ublas containers and algorithms which go beyond the 
original Vector/Matrix concepts.  That's not necessarily a problem, but 
if that's happened we should update the definitions of those concepts.

Thanks,
Shawn

Gunter Winkler wrote:

>On Tuesday 18 October 2005 22:51, Shawn D. Pautz wrote:
>  
>
>>Does the Matrix concept require a find2 member function?  My locally
>>defined matrix class does not work with lu_factorize (with pivots)
>>unless I provide that function.  Alternatively, do some of the ublas
>>algorithms have stronger requirements on the matrix classes than defined
>>by the Matrix concept?
>>    
>>
>
>Some matrix proxies (row and matrix_vector_range) use find2 to obtain 
>iterators pointing to begin and end of the data. To be more precise: nearly 
>all (const_)iterators use find to compute pointers to the data.
>
>I don't think find2 should be part of the matrix concept, because it is only 
>used internally. But if you create your own matrix class - you have to 
>provide this helper function.
>
>mfg
>GuWi
>
>  
>

-- 
Shawn D. Pautz
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Sandia National Laboratories
P.O. Box 5800
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E-Mail: sdpautz_at_[hidden]