Sievert integral
From specialfunctionswiki
The Sievert integral $S(z)$ is defined by $$S(z,\theta)=\int_0^{\theta} e^{-z \sec \phi} \mathrm{d} \phi,$$ where $e^{*}$ denotes the exponential and $\sec$ denotes secant.
Properties
Asymptotic behavior of Sievert integral
Relationship between Sievert integral and exponential integral E
Relationship between Sievert integral and Bessel K