function Psi2 = QM_PIBstep(V,E,Psi0,Psi1,dx)
% Psi2 = QM_PIBstep(V,E,Psi0,Psi1,dx);
% take a single step in space for PIB and TISE

Psi2 = 2*dx^2*(V-E)*Psi1 - Psi0 + 2*Psi1;

return