DOC: Write a doc string for special/mod.rs

src/special/mod.rs

@@ -1,4 +1,31 @@
-//! Special function module
+//! Special functions module
+//! 
+//! This module provides implementations of various special mathematical functions
+//! commonly used in statistical and scientific computing. It includes:
+//! 
+//! - Basic special functions:
+//!   - Gaussian (Normal) function
+//!   - Gamma function and its logarithm
+//!   - Pochhammer symbol (rising factorial)
+//! 
+//! - Incomplete special functions:
+//!   - Regularized incomplete gamma function and its inverse
+//!   - Regularized incomplete beta function and its inverse
+//! 
+//! - Error functions:
+//!   - Error function (erf) and its complement (erfc)
+//!   - Inverse error function and inverse complementary error function
+//! 
+//! - Other functions:
+//!   - Beta function
+//!   - Phi function (CDF of the standard normal distribution)
+//!   - Lambert W function (principal branch W₀ and secondary branch W₋₁)
+//! 
+//! Many of these functions are implemented using efficient numerical approximations
+//! or by wrapping functions from other crates (e.g., `puruspe`, `lambert_w`).
+//! 
+//! The module also includes an enum `LambertWAccuracyMode` to control the
+//! accuracy-speed trade-off for Lambert W function calculations.
 
 pub mod function;
 pub mod lanczos;