removed unused ritz_vectors and optimize DPR_free

[felipeZ]

fixed #34

[lopeztarifa]

Thanks @felipeZ!

The only thing missed is passing/using the residues in the correction vectors:

• correction = compute_DPR_free(matrixV, second_matrixV, eigenvalues_sub, eigenvectors_sub, diag_matrix, diag_second_matrix)

• correction = compute_DPR_generalized_dense(matrix, eigenvalues, ritz_vectors, second_matrix)

This is how it is implemented in Champ:

correction= compute_DPR( rs, parameters, eigenvalues_sub, diag_mtx, diag_stx)

Then in the compute_DPR function:

    diag = 0.0_dp
    do j = 1, parameters%basis_size 
     diag= eye( m , m, eigenvalues( j))
     correction( :, j)= rs( :, j) 

     do ii= 1, size( correction, 1)
       correction( ii, j)= correction( ii, j)/( eigenvalues( j)* diag_stx( ii)- diag_mtx( ii))
     end do

    end do