Re: [ublas] question regarding elementwise matrix product

Subject: Re: [ublas] question regarding elementwise matrix product
From: Kim Kuen Tang (kuentang_at_[hidden])
Date: 2009-05-28 16:19:08

Hi Kaveh,

Kaveh Kohan schrieb:
> Hi Kim,
>
> Thank you for your reply.
> I am sorry if my questions sounds naive. I ran into a problem 
> compiling this program. Do I need to have a specific version of 
> phoenix or spirit to compile this program. Since in my system, 
> phoenix.hpp is located in  "boost/spirit/phoenix.hpp", I changed your 
> program to the following:
This is not a good idea, because including only phoenix.hpp is not 
enough in your boost version.
( I use 1.39.)

>   symmetric_matrix<double,lower> m(3, 3), n(3,3), u(3,3);
>   generate(arg1, lambda[val(1.0)] )(m.data());
the plain data of your matrix is stored in the unbounded_array. Using 
the member data() you have access to this vector. Since you have another 
version of boost, i suggest you to change the above code to     
std::fill(m.data().begin(), m.data().end,1.0 ); This will have the same 
effect.
>   generate(arg1, lambda[val(2.0)] )(n.data());
>   
> transform(arg1,n.data().begin(),u.data().begin(),lambda[arg1/arg2])(m.data());
Using transform you can perform an element wise division. In blas there 
is already an element_wise division called element_div.
Here is the complete code:

# include <boost/numeric/ublas/symmetric.hpp>
# include <boost/numeric/ublas/matrix_expression.hpp>
# include <boost/numeric/ublas/io.hpp>

# include <vector>
# include <algorithm>

using namespace boost::numeric::ublas;

int main () {

    symmetric_matrix<double,lower> m(3, 3), n(3,3), u(3,3);
    std::fill(m.data().begin(), m.data().end(),1.0 );
    std::fill(n.data().begin(), n.data().end(),2.0 );
    u=element_div(m,n);
    std::cout << u << std::endl;
}
>
> Plus can you explain a little what it does because notation-wise, it 
> is very confusing for me. Definitely ignorance frommy side but I would 
> appreciate if you describe it a little bit.
>
> Thanks,
> Kaveh
>
> ------------------------------------------------------------------------
> **