WIP: Update document of solveh.rs

Drop module-level doc in solveh.rs

lax/src/solveh.rs

@@ -1,11 +1,15 @@
-//! Solve symmetric linear problem using the Bunch-Kaufman diagonal pivoting method.
-//!
-//! See also [the manual of dsytrf](http://www.netlib.org/lapack/lapack-3.1.1/html/dsytrf.f.html)
-
 use crate::{error::*, layout::MatrixLayout, *};
 use cauchy::*;
 use num_traits::{ToPrimitive, Zero};
 
+/// Solve symmetric linear problem using the Bunch-Kaufman diagonal pivoting method.
+///
+/// For a given symmetric matrix $A$,
+/// this method factorizes $A = U^T D U$ or $A = L D L^T$ where
+///
+/// - $U$ (or $L$) are is a product of permutation and unit upper (lower) triangular matrices
+/// - $D$ is symmetric and block diagonal with 1-by-1 and 2-by-2 diagonal blocks.
+///
 pub trait Solveh_: Sized {
     /// Bunch-Kaufman: wrapper of `*sytrf` and `*hetrf`
     fn bk(l: MatrixLayout, uplo: UPLO, a: &mut [Self]) -> Result<Pivot>;