From e312df1a7c8989101f494541a42c59d090922d6e Mon Sep 17 00:00:00 2001
From: Stefan Kroboth <stefan.kroboth@gmail.com>
Date: Wed, 7 Feb 2024 20:16:47 +0100
Subject: [PATCH] Added note to Eggholder Hessian docs

---
 crates/argmin-testfunctions/src/eggholder.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/crates/argmin-testfunctions/src/eggholder.rs b/crates/argmin-testfunctions/src/eggholder.rs
index ad8cc0525..00935dc31 100644
--- a/crates/argmin-testfunctions/src/eggholder.rs
+++ b/crates/argmin-testfunctions/src/eggholder.rs
@@ -97,6 +97,12 @@ where
 }
 
 /// Hessian of Eggholder test function
+///
+/// This function can return NaN elements under the following conditions:
+///
+/// * |x1 - x2 - 47| <= EPS && x1 != 0
+/// * |x2 - x1 + 47| <= EPS && x1 != 0
+/// * |x1/2 + x2 + 47| <= EPS && |x2 + 47| != 0
 pub fn eggholder_hessian<T>(param: &[T; 2]) -> [[T; 2]; 2]
 where
     T: Float + FromPrimitive,