Re: [ublas] Solving linear equations of the form Ax = b ?

From: Nico Galoppo (nico_at_[hidden])
Date: 2006-04-14 10:24:27

What I was saying is that, just as there are bindings for blas/lapack, there are 
bindings for atlas (imo a platform-optimized version of a subset of blas/lapack 
operations). There are bindings in
boost-sandbox/numeric/bindings/atlas

#include <boost/numeric/bindings/atlas/cblas1.hpp>
#include <boost/numeric/bindings/atlas/cblas2.hpp>
#include <boost/numeric/bindings/atlas/cblas3.hpp>
#include <boost/numeric/bindings/atlas/clapack.hpp>
#include <boost/numeric/bindings/traits/ublas_matrix.hpp>
#include <boost/numeric/bindings/traits/ublas_vector.hpp>
namespace atlas = boost::numeric::bindings::atlas;

std::vector<int> ipiv(matrix.size1());

int ierr = atlas::getrf(matrix, ipiv);
ierr = atlas::getrs(matrix, ipiv, rhs);

solves matrix * x = b where rhs stores b on input and receives x on output. 
atlas::getri(matrix, ipiv) does this in one step.

the documentation is in
boost-sandbox/libs/numeric/bindings/atlas/doc/index.html

--nico

Karl Meerbergen wrote:
> I suppose atlas is a compiled lapack. there are bindings in 
> boost-sandbox/numeric/bindings/lapack/gesv.hpp
> 
> #include <boost/numeric/bindings/traits/ublas_matrix.hpp>
> #include <boost/numeric/bindings/traits/ublas_vector2.hpp>
> #include <boost/numeric/bindings/lapack/gesv.hpp>
> 
> boost::numeric::bindings::lapack::gesv( matrix, rhs ) ;
> 
> solves matrix * x = b where rhs stores b on input and receives x on output.
> 
> for the factorization only (with singularity check), use:
> 
> #include <boost/numeric/bindings/traits/std_vector.hpp>
> std::vector<int> pivots( matrix.size1() ) ;
> int info = boost::numeric::bindings::lapack::getrfv( matrix, pivots )
> 
> Karl
> 
> 
> 
> Nico Galoppo wrote:
> 
> 
>>Have a look at the ATLAS bindings for ublas. ATLAS provides such factorization 
>>methods.
>>
>>http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?action=browse&id=Linear_Algebra_With_UBLAS&revision=15
>>
>>HTH,
>>
>>--nico
>>
>>John Maddock wrote:
>> 
>>
>>
>>>I gather from a quick web search that ublas does have LUP decomposition 
>>>routines, however a grep of the docs failed to find any mention of the 
>>>routine in question, and how they should be used.
>>>
>>>So.... does anyone have the boiler plate code needed to solve for x given 
>>>matrix A and vector b ?
>>>
>>>Many thanks,
>>>
>>>John Maddock. 
>>>
>>>_______________________________________________
>>>ublas mailing list
>>>ublas_at_[hidden]
>>>http://lists.boost.org/mailman/listinfo.cgi/ublas
>>>   
>>>
>>
>> 
>>
> 
> 
> 

-- 
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