From 3d57fbd094468cc2065f724dd3d0dcbb67cb8c85 Mon Sep 17 00:00:00 2001
From: Jon Santmyer <jon@jonsantmyer.com>
Date: Thu, 17 Nov 2022 17:27:52 -0500
Subject: initial commit. addition, subtraction, multiplication.

---
 matrix.hpp | 202 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 202 insertions(+)
 create mode 100644 matrix.hpp

diff --git a/matrix.hpp b/matrix.hpp
new file mode 100644
index 0000000..ada303b
--- /dev/null
+++ b/matrix.hpp
@@ -0,0 +1,202 @@
+#ifndef MATRIX_HPP
+#define MATRIX_HPP 1
+
+#include <array>
+#include <algorithm>
+#include <span>
+#include <ostream>
+
+template<typename T, std::size_t M, std::size_t N>
+    requires(std::is_arithmetic_v<T>)
+class matrix
+{
+protected:
+    std::array<T, N * M> v;
+public:
+    constexpr matrix(const std::array<std::array<T, N>, M> &vs)
+    {
+        for(std::size_t m = 0; m < M; m++)
+        for(std::size_t n = 0; n < N; n++) {
+            v[(m * N) + n] = vs[m][n];
+        }
+    }
+    constexpr matrix(const std::array<T, M * N> &vs) :
+        v(vs)
+    {}
+
+    constexpr matrix(T a) {
+        v.fill(a);
+    }
+
+    constexpr matrix &operator+=(const matrix &rhs)
+    {
+        for(std::size_t i = 0; i < M * N; i++)
+            v[i] += rhs.v[i];
+        return v;
+    }
+
+    constexpr friend matrix operator+(
+            matrix lhs, 
+            const matrix &rhs)
+    {
+        lhs += rhs;
+        return lhs;
+    }
+
+    constexpr friend matrix operator-(matrix lhs)
+    {
+        for(std::size_t i = 0; i < M * N; i++)
+            lhs.v[i] = -lhs.v[i];
+        return lhs;
+    }
+
+    constexpr matrix &operator-=(const matrix &rhs)
+    {
+        for(std::size_t i = 0; i < M * N; i++)
+            v[i] -= rhs.v[i];
+        return *this;
+    }
+
+    constexpr friend matrix operator-(
+            matrix lhs,
+            const matrix &rhs)
+    {
+        lhs -= rhs;
+        return lhs;
+    }
+
+    template<std::size_t P>
+    constexpr friend matrix<T, M, P> operator*(
+            const matrix<T, M, N> &rhs,
+            const matrix<T, N, P> &lhs)
+    {
+        matrix<T, M, P> ret(0);
+        for(std::size_t p = 0; p < P; p++) {
+            for(std::size_t m = 0; m < M; m++) {
+                for(std::size_t n = 0; n < N; n++) {
+                    ret.at(m, p) += rhs.at(m, n) * lhs.at(n, p);
+                }
+            }
+        }
+        return ret;
+    }
+
+    constexpr matrix &operator*=(const T &rhs)
+    {
+        std::ranges::transform(
+                v.begin(), 
+                v.end(), 
+                v.begin(), 
+                [rhs](T t) -> T { return t * rhs; }
+            );
+        return *this;
+    }
+
+    constexpr friend matrix operator*(
+            matrix lhs,
+            const T &rhs)
+    {
+        lhs *= rhs;
+        return lhs;
+    }
+
+    constexpr std::array<std::reference_wrapper<T>, N> row(std::size_t m)
+    {
+        std::array<std::reference_wrapper<T>, N> ret;
+        for(std::size_t n = 0; n < N; n++) ret[n] = v[(m * N) + n];
+        return ret;
+    }
+
+    constexpr std::array<std::reference_wrapper<T>, M> col(std::size_t n)
+    {
+        std::array<std::reference_wrapper<T>, M> ret;
+        for(std::size_t m = 0; m < M; m++) ret[m] = v[(m * M) + n];
+        return ret;
+    }
+
+    constexpr T &at(std::size_t m, std::size_t n)
+    {
+        return v.at((m * N) + n);
+    }
+    constexpr const T &at(std::size_t m, std::size_t n) const
+    {
+        return v.at((m * N) + n);
+    }
+
+    constexpr std::array<T, M * N> &data() noexcept { return v; }
+    constexpr std::array<T, M * N> &data() const noexcept { return v; }
+
+    constexpr friend std::ostream &operator<<(std::ostream &lhs, const matrix &rhs)
+    {
+        for(std::size_t m = 0; m < M; m++) {
+            lhs << '\n';
+            for(std::size_t n = 0; n < N; n++) {
+                lhs << rhs.at(m, n) << ", ";
+            }
+        }
+        return lhs;
+    }
+};
+
+template<typename T, std::size_t S>
+class sqmatrix final : public matrix<T, S, S>
+{
+    static constexpr sqmatrix identity()
+    {
+        sqmatrix ret(0);
+        for(std::size_t i = 0; i < S; i++) {
+            ret.at(i, i) = 1;
+        }
+        return ret;
+    }
+
+    constexpr sqmatrix operator*=(const sqmatrix &rhs)
+    {
+        sqmatrix copy(*this);
+        for(std::size_t i = 0; i < S; i++) {
+            for(std::size_t j = 0; j < S; j++) {
+                T cell = 0;
+                for(std::size_t k = 0; k < S; k++)
+                    cell += copy.at(k, j) * rhs.at(i, k);
+                this->at(i, j) = cell;
+            }
+        }
+        return *this;
+    }
+
+    constexpr friend sqmatrix operator*(
+            sqmatrix lhs,
+            const sqmatrix &rhs)
+    {
+        lhs *= rhs;
+        return lhs;
+    }
+};
+
+template<typename T, std::size_t L>
+class rowmatrix final : public matrix<T, L, 1>
+{
+    constexpr T &operator[](std::size_t i) const
+    {
+        return this->v[i];
+    }
+    constexpr T &operator[](std::size_t i)
+    {
+        return this->v[i];
+    }
+};
+
+template<typename T, std::size_t L>
+class colmatrix final : public matrix<T, 1, L>
+{
+    constexpr T &operator[](std::size_t i) const
+    {
+        return this->v[i];
+    }
+    constexpr T &operator[](std::size_t i)
+    {
+        return this->v[i];
+    }
+};
+
+#endif
-- 
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