cross-ref bunch-kaufman to ldlt docs (JuliaLang#43968)

Author: stevengj

stdlib/LinearAlgebra/src/ldlt.jl

@@ -129,10 +129,12 @@ end
 """
     ldlt(S::SymTridiagonal) -> LDLt
 
-Compute an `LDLt` factorization of the real symmetric tridiagonal matrix `S` such that `S = L*Diagonal(d)*L'`
+Compute an `LDLt` (i.e., ``LDL^T``) factorization of the real symmetric tridiagonal matrix `S` such that `S = L*Diagonal(d)*L'`
 where `L` is a unit lower triangular matrix and `d` is a vector. The main use of an `LDLt`
 factorization `F = ldlt(S)` is to solve the linear system of equations `Sx = b` with `F\\b`.
 
+See also [`bunchkaufman`](@ref) for a similar, but pivoted, factorization of arbitrary symmetric or Hermitian matrices.
+
 # Examples
 ```jldoctest
 julia> S = SymTridiagonal([3., 4., 5.], [1., 2.])