How to use Bessel function in C++?

please i need to put a source in FDTD program in C++ for HE11 mode
how can i use Bissel function in C++ and its modifecations ?

thanks

there r FDTD codes given in this board just search for them

please till me a bout one but it has to be related to HE11 mode

thanks

You need not consider HE11 mode exactly. Just launch properly polarized E or H field point source. If HE11 mode is dominant in your structure, it'll be set up automatically as wave propergates.