From 6e67ef2dc48a8aad3edc303213502dace9383adf Mon Sep 17 00:00:00 2001
From: Erik Schnetter <schnetter@gmail.com>
Date: Thu, 27 Jul 2023 11:55:09 -0400
Subject: [PATCH] Derivs: Correct 4th order deriv2_1d stencil

---
 Derivs/src/derivs.hxx | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Derivs/src/derivs.hxx b/Derivs/src/derivs.hxx
index 2b7b1a914..cc9384902 100644
--- a/Derivs/src/derivs.hxx
+++ b/Derivs/src/derivs.hxx
@@ -248,10 +248,11 @@ inline CCTK_ATTRIBUTE_ALWAYS_INLINE
   // constexpr T c2 = -1 / T(12);
   // return (c2 * (var(-2) + var(2)) + c1 * (var(-1) + var(1)) + c0 * var(0)) /
   //        pow2(dx);
-  const T c0 = 15 / (12 * pow2(dx));
-  const T c1 = -1 / (12 * pow2(dx));
-  return c1 * ((var(4) - var(1)) - (var(3) - var(0))) +
-         c0 * ((var(3) - var(2)) - (var(2) - var(1)));
+  constexpr T c0 = 4 / T(3);
+  constexpr T c1 = -1 / T(12);
+  return (c1 * ((var(+2) - var(+0)) - (var(-0) - var(-2))) +
+          c0 * ((var(+1) - var(+0)) - (var(-0) - var(-1)))) /
+         pow2(dx);
 }
 
 template <int deriv_order, bool vectorize_di, typename T, typename TS,