Hello;

I need some help to compute the series approximation of the modulus and argument of hankel function for large x. The code display

Error, (in asympt) unable to compute series

Thanks for helping me.

#We define the hankel function as

#HankelH1(v,x) = BesselJ(v,x) + I*BesselY(v,x), where BesselJ and BesselY are bessel function.

#In this question the parameter "v " is fixed. "

# Code

restart:

with(MTM):

HankelH1(v, x);

# The modulus of Hankel function

Mn:=x->abs(HankelH1(v, x));

thetan:=x->argument(HankelH1(v, x));

phin:=x->argument(diff(HankelH1(v, x),x));

dervthetan:=x->diff(thetan(x),x);

dervphin:=x->diff(phin(x),x);

# Compute series

series(thetan(x),x=infinity,7);

series(phin(x),x=infinity,7);

series(Nn(x),x=infinity, 7);

series(Mn(x),x=infinity,7);

# I define the following function

f:=x->(Nm(x)/Mn(x))*exp(I*(phin(x)-thetan(x)));

# Series approximation

series(f(x),x=infinity, 7);