# Kelvin ker

The $\mathrm{ker}_{\nu}$ function is defined as $$\mathrm{ker}_{\nu}(z)=\mathrm{Re} \left[ e^{-\frac{\nu \pi i}{2}} K_{\nu} \left( z e^{\frac{\pi i}{4}} \right) \right],$$ where $\mathrm{Re}$ denotes the real part of a complex number and $K_{\nu}$ denotes the modified Bessel function $K_{\nu}$.