From bc4f061bcd4d9240b2ea43fbebae84d72f5c9006 Mon Sep 17 00:00:00 2001
From: Jon Janzen <jonjanzen@me.com>
Date: Fri, 2 Apr 2021 13:56:19 -0600
Subject: [PATCH] added submatrixes

had to use in development features to allow math with const generics
---
 matrix/src/lib.rs | 55 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/matrix/src/lib.rs b/matrix/src/lib.rs
index 260d075..2243c17 100644
--- a/matrix/src/lib.rs
+++ b/matrix/src/lib.rs
@@ -1,3 +1,6 @@
+#![feature(const_generics)]
+#![feature(const_evaluatable_checked)]
+#![allow(incomplete_features)]
 #[macro_use]
 extern crate approx;
 
@@ -11,6 +14,7 @@ pub struct Matrix<const H: usize, const W: usize> {
 }
 
 impl<const H: usize, const W: usize> Matrix<H, W> {
+
     pub fn default() -> Self {
         Matrix {
             matrix: [[0f32; W]; H],
@@ -46,6 +50,24 @@ impl<const H: usize, const W: usize> Matrix<H, W> {
     pub fn determinant(&self) -> f32 {
         self.matrix[0][0] * self.matrix[1][1] - self.matrix[0][1] * self.matrix[1][0]
     }
+
+    pub fn sub_matrix(&self, skip_row: usize, skip_col: usize) -> Matrix<{H - 1}, {W - 1}> 
+    {
+        let mut idx_row: usize = 0;
+
+        let mut arr = [[0f32; W - 1]; H - 1];
+        for (i, row) in self.matrix.iter().enumerate().take(W) {
+            if i == skip_row { continue; }
+            let mut idx_col: usize = 0;
+            for (j, col) in row.iter().enumerate().take(W) {
+                if j == skip_col { continue; }
+                arr[idx_row][idx_col] = *col;
+                idx_col += 1;
+            }
+            idx_row += 1;
+        }
+        Matrix::from_array(arr)
+    }
 }
 
 impl<const H: usize, const W: usize> Index<usize> for Matrix<H, W> {
@@ -336,4 +358,37 @@ mod tests {
 
         assert_eq!(17.0, m.determinant());
     }
+
+    #[test]
+    fn submatrix_3x3() {
+        let start = Matrix::from_array([
+            [1.0, 5.0, 0.0],
+            [-3.0, 2.0, 7.0],
+            [0.0, 6.0, -3.0],
+        ]);
+
+        let expected = Matrix::from_array([
+            [-3.0, 2.0],
+            [0.0, 6.0],
+        ]);
+
+        assert_eq!(expected, start.sub_matrix(0, 2));
+    }
+
+    #[test]
+    fn submatrix_4x4() {
+        let start = Matrix::from_array([
+            [-6.0, 1.0, 1.0, 6.0],
+            [-8.0, 5.0, 8.0, 6.0],
+            [-1.0, 0.0, 8.0, 2.0],
+            [-7.0, 1.0, -1.0, 1.0],
+        ]);
+        let expected = Matrix::from_array([
+            [-6.0, 1.0, 6.0],
+            [-8.0, 8.0, 6.0],
+            [-7.0, -1.0, 1.0],
+        ]);
+
+        assert_eq!(expected, start.sub_matrix(2, 1));
+    }
 }