Kelvin ber

The $\mathrm{ber}_{\nu}$ function is defined as $$\mathrm{ber}_{\nu}(z)=\mathrm{Re} \hspace{2pt} J_{\nu} \left( z e^{\frac{3\pi i}{4}} \right),$$ where $\mathrm{Re}$ denotes the real part of a complex number and $J_{\nu}$ denotes the Bessel function of the first kind.