From efd5b5bea4640e498686f1c7f2eae44d2caad44b Mon Sep 17 00:00:00 2001
From: Jaron Kent-Dobias <jaron@kent-dobias.com>
Date: Mon, 10 Feb 2025 08:24:43 -0300
Subject: Slightly more effecient calculation of gradient

---
 fits.cpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fits.cpp b/fits.cpp
index 370b63d..62d75c9 100644
--- a/fits.cpp
+++ b/fits.cpp
@@ -57,11 +57,12 @@ Real cost(const std::list<std::tuple<Real, Real>>& data, const Vector& coeffs) {
 Vector dCost(const std::list<std::tuple<Real, Real>>& data, const Vector& coeffs) {
   Vector dC = Vector::Zero(coeffs.size());
 
-  for (unsigned j = 0; j < coeffs.size(); j++) {
-    for (const std::tuple<Real, Real>& xy : data) {
+  for (const std::tuple<Real, Real>& xy : data) {
+    for (unsigned j = 0; j < coeffs.size(); j++) {
       Real x = std::get<0>(xy);
       Real y = std::get<1>(xy);
-      dC[j] += (value(coeffs, x) - y) * basisFunctions(coeffs.size(), j, x);
+      Real Δc = value(coeffs, x) - y;
+      dC[j] += Δc * basisFunctions(coeffs.size(), j, x);
     }
   }
 
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