Jacobi cs
From specialfunctionswiki
The $\mathrm{cs}$ function is defined by $$\mathrm{cs}(u)=\dfrac{\mathrm{cn}(u)}{\mathrm{sn}(u)},$$ where $\mathrm{cn}$ is the Jacobi cn function and $\mathrm{sn}$ is the Jacobi sn function.
Domain coloring of $\mathrm{cs}$ corresponding to $m=0.8$.
References
Special functions by Leon Hall