From 58ac3feb56d3dda792d80fa6f8b010d5472706ef Mon Sep 17 00:00:00 2001
From: Mael <mael.bianchi@etu.unistra.fr>
Date: Fri, 20 Mar 2026 15:29:28 +0100
Subject: [PATCH] Fixed element for lower triangular part of BTDMatrix

---
 .../LinearAlgebra/src/sofa/linearalgebra/BTDMatrix.inl          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Sofa/framework/LinearAlgebra/src/sofa/linearalgebra/BTDMatrix.inl b/Sofa/framework/LinearAlgebra/src/sofa/linearalgebra/BTDMatrix.inl
index cf83888d768..bc8a9865d66 100644
--- a/Sofa/framework/LinearAlgebra/src/sofa/linearalgebra/BTDMatrix.inl
+++ b/Sofa/framework/LinearAlgebra/src/sofa/linearalgebra/BTDMatrix.inl
@@ -121,7 +121,7 @@ SReal BTDMatrix<N, T>::element(Index i, Index j) const
     const Index bi = i / BSIZE; i = i % BSIZE;
     const Index bj = j / BSIZE; j = j % BSIZE;
     const Index bindex = bj - bi + 1;
-    if (bindex >= 3) return (SReal)0;
+    if (bindex >= 3 || bindex < 0) return (SReal)0;
     return data[bi*3+bindex](i,j);
 }