Riemann-Siegel theta function
From specialfunctionswiki
The Riemann-Siegel theta function is defined by $$\theta(t)= \arg \left( \Gamma \left( \dfrac{2it+1}{4} \right) \right) - \dfrac{\log \pi}{2}t,$$ where $\Gamma$ denotes the Gamma function and $\log$ denotes the logarithm.
