functiontaup=taupf(tau,e2)%TAUPF tan(chi)%% TAUPF(tau, e2) returns tangent of chi in terms of tau the tangent of% phi. e2, the square of the eccentricity, is a scalar; taup can be any% shape.tau1=hypot(1,tau);sig=sinh(eatanhe(tau./tau1,e2));taup=hypot(1,sig).*tau-sig.*tau1;end