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