How to obtain eigenvalue of two-site reduced density matrix

Question

I calculate two-site reduced density matrix from a MPS , just like

//index linking i to i+1:
auto ir = commonIndex(psi.A(i),psi.A(i+1));

auto rho = psi.A(i)*dag(prime(psi.A(i),Site,ir));
for(int k = i+1; k < j; ++k)
{
rho *= psi.A(k);
rho *= dag(prime(psi.A(k),Link));
}
rho *= psi.A(j);
rho *= dag(prime(psi.A(j)));
for(int k = j+1; k <= psi.N(); ++k)
{
rho *= psi.A(k);
rho *= dag(prime(psi.A(k),Link));
}
How can I obtain eigenvalue of \rho

Answer 1

Hi JR,
The diagHermitian function should be what you need. You can read more about it on this page:
http://itensor.org/docs.cgi?vers=cppv2&page=classes/decomp

Comments

thanks a lot!