Function EigensystemTridiagonal(bool, vector<double>&, vector<double>&, vector<double>&, vector<double>&)

• Defined in File Lanczos.hpp

Function Documentation

void EigensystemTridiagonal(bool evector_flag, vector<double> &alpha, vector<double> &beta, vector<double> &energy, vector<double> &evector)

From the Lanczos coefficients alpha and beta, returns the lowest eigenvalue and the corresponding eigenvector in the Lanczos (reduced) basis.

if evector_flag = false, calculates lowest eigenvalue only (no eigenvector); otherwise also calculates the associated eigenvector

Parameters:

• evector_flag – flag for the calculation of the eigenvector

• alpha – Diagonal

• beta – Second diagonal

• energy – eigenvalues (not pre-allocated)

• evector – lowest eigenvector in the reduced basis (not pre-allocated)