From 4c7c27a0298e98dce2ac0ef1b8ce293b08446374 Mon Sep 17 00:00:00 2001
From: Chris Elrod <elrodc@gmail.com>
Date: Thu, 15 Feb 2024 21:17:33 -0500
Subject: [PATCH] add operator<<(std::ostream, Dual)

---
 include/Math/Dual.hpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/Math/Dual.hpp b/include/Math/Dual.hpp
index deb594a..7bd2a12 100644
--- a/include/Math/Dual.hpp
+++ b/include/Math/Dual.hpp
@@ -8,6 +8,7 @@
 #include <Math/StaticArrays.hpp>
 #include <Utilities/Invariant.hpp>
 #include <cstddef>
+#include <istream>
 #include <utility>
 
 namespace poly::math {
@@ -824,6 +825,14 @@ constexpr auto dval(Dual<T, N> &x) -> double & {
   return dval(x.value());
 }
 
+template <typename T, ptrdiff_t N>
+auto operator<<(std::ostream &os, const Dual<T, N> &x) -> std::ostream & {
+  os << "Dual<" << N << ">{" << x.value();
+  for (ptrdiff_t n = 0; n < N; ++n) os << ", " << x.gradient()[n];
+  os << "}";
+  return os;
+};
+
 class GradientResult {
   double x;
   MutPtrVector<double> grad;