From 3527c75ad2cff62e259553559ac6aff5ebc29e69 Mon Sep 17 00:00:00 2001
From: Xavier Andrade <xavier@tddft.org>
Date: Tue, 15 Oct 2024 11:47:11 -0700
Subject: [PATCH 1/5] Make the zero class simpler using the empty constructor.

---
 src/math/zero.hpp | 32 +-------------------------------
 1 file changed, 1 insertion(+), 31 deletions(-)

diff --git a/src/math/zero.hpp b/src/math/zero.hpp
index 8fbfa1cde..80ecee26b 100644
--- a/src/math/zero.hpp
+++ b/src/math/zero.hpp
@@ -21,37 +21,7 @@ namespace inq {
 
 template <typename Type>
 GPU_FUNCTION auto zero(){
-  return Type{0.0};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<double>>(){
-  return vector3<double>{0.0, 0.0, 0.0};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<double, covariant>>(){
-  return vector3<double, covariant>{0.0, 0.0, 0.0};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<double, contravariant>>(){
-  return vector3<double, contravariant>{0.0, 0.0, 0.0};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<complex>>(){
-  return vector3<complex>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<complex, covariant>>(){
-  return vector3<complex, covariant>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}};
-}
-
-template <>
-GPU_FUNCTION auto zero<vector3<complex, contravariant>>(){
-  return vector3<complex, contravariant>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}};
+  return Type{};
 }
 
 }

From 282da432dd23a395ab27509f3f5cf93fd69adc49 Mon Sep 17 00:00:00 2001
From: Xavier Andrade <xavier@tddft.org>
Date: Tue, 15 Oct 2024 11:48:07 -0700
Subject: [PATCH 2/5] Check that zero works.

---
 src/math/zero.hpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/math/zero.hpp b/src/math/zero.hpp
index 80ecee26b..8795cbb7a 100644
--- a/src/math/zero.hpp
+++ b/src/math/zero.hpp
@@ -33,6 +33,11 @@ GPU_FUNCTION auto zero(){
 #include <catch2/catch_all.hpp>
 
 TEST_CASE(INQ_TEST_FILE, INQ_TEST_TAG) {
-  
+	using namespace inq;
+	
+	CHECK(zero<double>() == 0.0);
+	CHECK(zero<complex>() == complex{0.0, 0.0});
+	CHECK(zero<vector3<double>>() == vector3<double>{0.0, 0.0, 0.0});
+	CHECK(zero<vector3<complex>>() == vector3<complex>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}});
 }
 #endif

From a0a305f0e31d535b2e6fcdd8e341f1c0c287cc5d Mon Sep 17 00:00:00 2001
From: Xavier Andrade <xavier@tddft.org>
Date: Tue, 15 Oct 2024 12:18:18 -0700
Subject: [PATCH 3/5] Declare zero constrexpr.

---
 src/math/zero.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/math/zero.hpp b/src/math/zero.hpp
index 8795cbb7a..01acf4d54 100644
--- a/src/math/zero.hpp
+++ b/src/math/zero.hpp
@@ -20,7 +20,7 @@
 namespace inq {
 
 template <typename Type>
-GPU_FUNCTION auto zero(){
+GPU_FUNCTION constexpr auto zero(){
   return Type{};
 }
 

From c69402f9b1ca1c5cd1f70b876a1e9e167316d4a1 Mon Sep 17 00:00:00 2001
From: Xavier Andrade <xavier@tddft.org>
Date: Tue, 15 Oct 2024 12:21:51 -0700
Subject: [PATCH 4/5] Make a non-template zero() function that works for
 comparison.

---
 src/math/zero.hpp | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/math/zero.hpp b/src/math/zero.hpp
index 01acf4d54..b5630e123 100644
--- a/src/math/zero.hpp
+++ b/src/math/zero.hpp
@@ -24,6 +24,23 @@ GPU_FUNCTION constexpr auto zero(){
   return Type{};
 }
 
+struct zero_t {
+};
+
+auto zero() {
+	return zero_t{};
+}
+
+template <typename Type>
+auto operator==(Type const & aa, zero_t) {
+	return aa == zero<Type>();
+}
+
+template <typename Type>
+auto operator==(zero_t z, Type const & aa) {
+	return aa == z;
+}
+
 }
 #endif
 
@@ -39,5 +56,15 @@ TEST_CASE(INQ_TEST_FILE, INQ_TEST_TAG) {
 	CHECK(zero<complex>() == complex{0.0, 0.0});
 	CHECK(zero<vector3<double>>() == vector3<double>{0.0, 0.0, 0.0});
 	CHECK(zero<vector3<complex>>() == vector3<complex>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}});
+	
+	CHECK(zero() == 0.0);
+	CHECK(zero() == complex{0.0, 0.0});
+	CHECK(zero() == vector3<double>{0.0, 0.0, 0.0});
+	CHECK(zero() == vector3<complex>{complex{0.0, 0.0}, complex{0.0, 0.0}, complex{0.0, 0.0}});
+
+	//	double aa = zero();
+	//	CHECK(aa == 0.0);
+	
 }
+
 #endif

From 788e5d47057ab9aa6ffe5c838ab371fc36220c19 Mon Sep 17 00:00:00 2001
From: Xavier Andrade <xavier@tddft.org>
Date: Tue, 15 Oct 2024 14:03:57 -0700
Subject: [PATCH 5/5] Avoid ambiguity for thrust::complex values.

---
 src/math/zero.hpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/math/zero.hpp b/src/math/zero.hpp
index b5630e123..6bda4ea8e 100644
--- a/src/math/zero.hpp
+++ b/src/math/zero.hpp
@@ -31,11 +31,19 @@ auto zero() {
 	return zero_t{};
 }
 
+auto operator==(complex const & aa, zero_t) {
+	return aa == zero<complex>();
+}
+
 template <typename Type>
 auto operator==(Type const & aa, zero_t) {
 	return aa == zero<Type>();
 }
 
+auto operator==(zero_t z, complex const & aa) {
+	return aa == z;
+}
+
 template <typename Type>
 auto operator==(zero_t z, Type const & aa) {
 	return aa == z;