Re: [ublas] find2 required by Matrix?

From: Shawn D. Pautz (sdpautz_at_[hidden])
Date: 2005-10-19 10:16:04

All,

Here's some more information that may be relevant to this discussion.  
The code below does not compile with gcc 3.2.3 (I've suppressed the 
include statements; I've tried including a lot of the ublas header files 
without success).  Which lines ought to work, and which lines are an 
error on my part?

int main()
{
    ublas::matrix<double> A(2,2);
    ublas::matrix<double> B(2,2);
    lu_factorize(A);   // compiles
    lu_factorize(B);   // compiles
    lu_factorize(ublas::prod(A,B));   // won't compile
    lu_factorize(ublas::matrix<double>(ublas::prod(A,B)));  // won't compile
    lu_factorize(static_cast<ublas::matrix<double> 
 >(ublas::prod(A,B)));  // won't compile
    ublas::matrix<double> tempMatrix(ublas::prod(A,B));   // compiles
    lu_factorize(tempMatrix);   // compiles
}

The compiler complains about not being able to convert the result of 
prod into a matrix<double> unless I make an explicit temporary.  Is that 
the intended usage of lu_factorize, or should I be able to nest the 
operations in one line?  I prefer the compact expression if I can get it 
to work.

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
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E-Mail: sdpautz_at_[hidden]