From d09a99faaea91f6f988e0015521d54c38cf4f0f0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattia=20Isgr=C3=B2?= <mattiaisgro@users.noreply.github.com>
Date: Tue, 30 Apr 2024 18:01:44 +0200
Subject: [PATCH] Add sparse vector first implementation

---
 examples/example.cpp     |  22 ++++---
 src/algebra/sparse_vec.h | 124 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 139 insertions(+), 7 deletions(-)
 create mode 100644 src/algebra/sparse_vec.h

diff --git a/examples/example.cpp b/examples/example.cpp
index 71f147d84..8b41e4810 100644
--- a/examples/example.cpp
+++ b/examples/example.cpp
@@ -7,16 +7,24 @@
 #include "theoretica.h"
 using namespace th;
 
+#include "algebra/sparse_vec.h"
+
+
 int main() {
     
-    // Declare a 3D vector
-    vec3 v = {1, 2, 3};
+    sparse_vec<> v1 = sparse_vec<>({
+        vec2({1, PI}), vec2({9, PHI})
+    });
 
-    // Create a 3x3 identity matrix
-    mat3 A = mat3::identity();
+    sparse_vec<> v2 = sparse_vec<>({
+        vec2({1, 3.0})
+    });
 
-    // Transform v by A
-    vec3 w = A * v;
- 
+    std::cout << v1 << std::endl;
+    std::cout << v2 << std::endl;
+    std::cout << v1 * v2 << std::endl;
+    
+    char c;
+    std::cin >> c;
     return 0;
 }
diff --git a/src/algebra/sparse_vec.h b/src/algebra/sparse_vec.h
new file mode 100644
index 000000000..4fc56d0bc
--- /dev/null
+++ b/src/algebra/sparse_vec.h
@@ -0,0 +1,124 @@
+
+///
+/// @file sparse_vec.h Sparse vector class implemented as a hashmap
+///
+
+#ifndef THEORETICA_SPARSE_VEC_H
+#define THEORETICA_SPARSE_VEC_H
+
+#include <map>
+#include "../core/constants.h"
+
+
+namespace theoretica {
+
+	/// @class sparse_vec Sparse vector class implemented as a hashmap
+	template<typename T = real, typename IndexType = size_t>
+	class sparse_vec {
+		public:
+
+			/// Data is stored in a hashmap as (index, value)
+			std::map<IndexType, T> data;
+
+
+			/// Initialize as the zero vector
+			sparse_vec() {}
+			
+
+			/// Initialize the sparse vector from a list
+			/// of pairs (index, value)
+			template<typename Pair>
+			sparse_vec(const std::initializer_list<Pair>& pairs) {
+
+				for (auto& pair : pairs)
+					data[pair[0]] = pair[1];
+			}
+
+
+			~sparse_vec() = default;
+
+
+			/// Add two sparse vectors
+			inline sparse_vec<T> operator+(const sparse_vec<T>& other) {
+
+				sparse_vec res;
+				res.data = this->data;
+
+				for (auto& pair : other)
+					res[pair.first] += pair.second;
+
+				return res;
+			}
+
+
+			/// Dot product of two sparse vectors
+			inline T operator*(const sparse_vec<T>& other) {
+
+				T res = T(0.0);
+
+				for (auto& pair : data)
+					res += pair.second * other[pair.first];
+
+				return res;
+			}
+
+
+			/// Get the n-th element
+			inline T operator[](IndexType index) const {
+
+				const auto iter = data.find(index);
+
+				if(iter == data.end())
+					return 0;
+
+				return iter->second;
+			}
+
+
+			/// Access the n-th element
+			inline T& operator[](IndexType index) {
+				return data[index];
+			}
+
+
+#ifndef THEORETICA_NO_PRINT
+
+		/// Convert the vector to string representation
+		inline std::string to_string(
+			const std::string& separator = ", ",
+			bool parenthesis = true) const {
+
+			std::stringstream res;
+
+			// if(parenthesis)
+			// 	res << "(";
+
+			for (auto& pair : this->data) {
+				// res << pair.second;
+				// res << separator;
+
+				res << "(" << pair.first << ", "
+					<< pair.second << ") ";
+
+			}
+
+			// if(parenthesis)
+			// 	res << ")";
+
+			return res.str();
+		}
+
+
+		/// Stream the vector in string representation to an output stream (std::ostream)
+		inline friend std::ostream& operator<<(
+			std::ostream& out, const sparse_vec<T>& obj) {
+			return out << obj.to_string();
+		}
+
+#endif
+
+	};
+
+}
+
+#endif