Re: [ALPS-users] Printing out Eigenvector

On 3 Sep 2010, at 03:23, rexlundgren@mail.utexas.edu wrote:

Hi, Thanks for the reply. When I try that with the following code inserted in the sparsediag.h file :

//orignal code

 // calculate eigen vectors
 ietl::Info<magnitude_type> info; // (m1, m2, ma, eigenvalue, residualm, status).

 try {
   eigenvectors.clear();
   lanczos.eigenvectors(lanczos.eigenvalues().begin(),lanczos.eigenvalues().begin()+n,
                        std::back_inserter(eigenvectors),info,generator);


 }
 catch (std::runtime_error& e) {
   std::cout <<"Exception during eigenvector calculation: " <<  e.what() << "\n";

 }

} else { vector_type v(1); v[0]=1.; eigenvectors.push_back(v);

//new code to print out eigenvectors
std::cout << eigenvectors[0].size() << " Size \n";
std::cout << eigenvectors[0] << "\n";

}

} // rest of code

The output is the following for a spin chain with L=4.

1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) Starting Lanczos Finished Lanczos 1 Size [1]((1,0)) Starting Lanczos Finished Lanczos 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0)) 1 Size [1]((1,0))

The problem is I don't know how to interpret this in terms of the original basis that is not within the subspace, or if there is still some problem in my code(maybe its in the wrong spot).

Thanks for the help

Rex

You should print the parameters (from the variable parms) as well - they give the quantum numbers, such as Sz and the TOTAL_MOMENTUM. For the small system you looked at most subspaces are of size 1, that's why you just get 1-dimensional eigenvectors.

Matthias