[ublas] [Question] sub-matrix by columns

Subject: [ublas] [Question] sub-matrix by columns
From: Marcel Rehberg (Marcel.Rehberg_at_[hidden])
Date: 2010-11-19 11:04:29

Hello,

I have a rather large matrix and I try to access submatrices based on  
columns. For example I would like to access the 3rd, 5th, and 9th column.  
Since the intervals between the columns I need are not regular a basic  
stride won't work. I'd figured I could use the more general  
matrix_indirect however I couldn't get that to work, plus I would have to  
index the rows too, which would be unnecessary.

I guess I could also use a large combination of two element strides but  
how does that inflict on performance?

My last resort would be to rearrange the columns to a more regular order  
and try to use strides then.

Or maybe I just overlooking a most basic and simple solution.

btw: Regarding the error for the matrix_indirect: For indexing I tried to  
use ublas::matrix<unsigned> but that got me several

boost_1_44_0/boost/numeric/ublas/matrix_proxy.hpp:4381: error: no type  
named ‘const_iterator’ in ‘class boost::numeric::ublas::matrix<unsigned  
int, boost::numeric::ublas::basic_row_major<unsigned int, int>,  
boost::numeric::ublas::unbounded_array<unsigned int,  
std::allocator<unsigned int> > >’

and

boost/numeric/ublas/matrix_proxy.hpp:4220: error: ‘const class  
boost::numeric::ublas::matrix<unsigned int,  
boost::numeric::ublas::basic_row_major<unsigned int, int>,  
boost::numeric::ublas::unbounded_array<unsigned int,  
std::allocator<unsigned int> > >’ has no member named ‘preprocess’

However, I tried also matrix_vector_indirect with ublas::vector<unsigned>  
for indexing and it worked.

Thanks for any help.

Marcel

-- 
Marcel Rehberg
Center for Systems Biology (ZBSA)
AG Modeling and Scientific Computing
Habsburger Str. 49
79104 Freiburg
Germany
phone: [phone]
http://omnibus.uni-freiburg.de/~dl954/