Add special::Bessel trait

sci-rs/src/special/bessel.rs

@@ -0,0 +1,24 @@
+/// All [functions located in the `Faster versions of common Bessel
+/// functions.`](<https://docs.scipy.org/doc/scipy/reference/special.html#faster-versions-of-common-bessel-functions>)
+pub trait Bessel {
+    /// Modified Bessel function of order 0.
+    ///
+    /// ## Notes
+    /// * The range is partitioned into the two intervals [0, 8] and (8, infinity).
+    /// * [Scipy has this as a
+    ///   ufunc](<https://docs.scipy.org/doc/scipy/reference/special.html#special-functions-scipy-special>),
+    ///   as a supposed wrapper over the Cephes routine. We try to define it over reasonable types in
+    ///   the impl.
+    ///
+    fn i0(&self) -> Self;
+
+    /// Exponentially scaled modified Bessel function of order 0.
+    ///
+    /// ## Notes
+    /// * The range is partitioned into the two intervals [0, 8] and (8, infinity).
+    /// * [Scipy has this as a
+    ///   ufunc](<https://docs.scipy.org/doc/scipy/reference/special.html#special-functions-scipy-special>),
+    ///   as a supposed wrapper over the Cephes routine. We try to define it over reasonable types in
+    ///   the impl.
+    fn i0e(&self) -> Self;
+}