# [Boost-users] How to do svd for a complex matrix using ublas & lapack bindings?

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### Allen Chen

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Dec 24, 2008, 10:21:17 AM12/24/08
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Hi,

Today I begin to learn to use boost ublas.
And I have successfully done svd for a real matrix. To do svd for a
complex matrix, I simply change codes from double to std::complex like
the following.
But it does not work.

#include <boost/numeric/bindings/lapack/gesdd.hpp>
#include<boost/numeric/bindings/traits/ublas_matrix.hpp>
#include<boost/numeric/bindings/traits/ublas_vector.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/vector.hpp>

int main()
{
using namespace boost::numeric::bindings::lapack;
using namespace boost::numeric::ublas;

matrix<std::complex<double>, column_major> A (4,2);
A(0,0)=std::complex<double>(2, 5);
A(0,1)=4;
A(1,0)=1;
A(1,1)=3;
A(2,0)=0;
A(2,1)=0;
A(3,0)=0;
A(3,1)=0;

std::cout << A << std::endl;

matrix<std::complex<double>, column_major> U(4,4);
matrix<std::complex<double>, column_major> V(2,2);
vector<std::complex<double>> S(2);
gesdd(A, S, U, V);

std::cout << U << std::endl;
std::cout << S << std::endl;
std::cout << V << std::endl;

return 0;
}

When compiles the program, MSVC8 will tell that it found no gesdd
method for complex type arguments.
Please help me.
Thanks

Allen
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### Thomas Klimpel

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Dec 25, 2008, 7:39:52 AM12/25/08
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Hi Allen,

Allen Chen wrote:
> Today I begin to learn to use boost ublas.

There is also a mailing list especially for boost ublas.

> And I have successfully done svd for a real matrix.
> To do svd for a complex matrix, I simply change codes
> from double to std::complex like the following.
> But it does not work.

The singular values "S" are still real, even for a complex matrix. So you should write "vector<double> S(2);" instead of "vector<std::complex<double>> S(2);".

Regards,
Thomas

winmail.dat

### Allen Chen

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Dec 25, 2008, 9:32:35 AM12/25/08
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2008/12/25 Thomas Klimpel <Thomas....@synopsys.com>:

> Hi Allen,
>
> Allen Chen wrote:
>> Today I begin to learn to use boost ublas.
>
>There is also a mailing list especially for boost ublas.

Thanks! I will join the mailing list.

>
>> And I have successfully done svd for a real matrix.
>> To do svd for a complex matrix, I simply change codes
>> from double to std::complex like the following.
>> But it does not work.
>
> The singular values "S" are still real, even for a complex matrix. So you should write "vector<double> S(2);" instead of "vector<std::complex<double>> S(2);".
>

Oh, that's great, it does work now.
I forget the thing that singual value is already real.
Thank you very much.

Merry christmas!

Allen

> Regards,
> Thomas

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