Re: [Vxl-users] How to get eigenvalue and eigenvector of a symmetric matrix

[Peter V. <Pet...@es...>]

> I am new to VXL, I want to compute the eigenvalue and eigenvector from
> 3x3 Hessian Matrix, but I do know how to compute using VXL, could you
> give me some example illustrating how to do this in VXL?

Did you try using vnl/algo/vnl_symmetric_eigensystem ?


Here is an example of use, distilled from vnl/tests/test_symmetric_eigensystem.cxx :

#include <vcl_iostream.h>
#include <vnl/algo/vnl_symmetric_eigensystem.h>

int main()
{
  double Sdata[36] = {
   30.0000,   -3.4273,   13.9254,   13.7049,   -2.4446,   20.2380,
   -3.4273,   13.7049,   -2.4446,    1.3659,    3.6702,   -0.2282,
   13.9254,   -2.4446,   20.2380,    3.6702,   -0.2282,   28.6779,
   13.7049,    1.3659,    3.6702,   12.5273,   -1.6045,    3.9419,
   -2.4446,    3.6702,   -0.2282,   -1.6045,    3.9419,    2.5821,
   20.2380,   -0.2282,   28.6779,    3.9419,    2.5821,   44.0636,
  };
  vnl_matrix<double> S(Sdata, 6,6);

  vnl_symmetric_eigensystem<double> eig(S);
  vcl_cout<<"Eigenvalues: ";
  for (int i=0;i<6;++i)
    vcl_cout<<eig.get_eigenvalue(i)<<' ';
  vcl_cout<<vcl_endl;
}


--	Peter.