From 38c5c284544282c804803934f14d543d9b096aa9 Mon Sep 17 00:00:00 2001
From: Palash Tyagi <23239946+Magnus167@users.noreply.github.com>
Date: Thu, 1 May 2025 23:10:51 +0100
Subject: [PATCH] Enhance matrix assertions for row and column operations to
 allow 0-row matrices with empty columns and improve error messages for index
 out of bounds.

---
 src/matrix/mat.rs | 62 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 53 insertions(+), 9 deletions(-)

diff --git a/src/matrix/mat.rs b/src/matrix/mat.rs
index 02a042b..07a3d3d 100644
--- a/src/matrix/mat.rs
+++ b/src/matrix/mat.rs
@@ -14,7 +14,11 @@ impl<T: Clone> Matrix<T> {
         let cols = cols_data.len();
         assert!(cols > 0, "need at least one column");
         let rows = cols_data[0].len();
-        assert!(rows > 0, "need at least one row");
+                                                            // Allow 0-row matrices if columns are empty, but not 0-col matrices if rows > 0
+        assert!(
+            rows > 0 || cols == 0,
+            "need at least one row if columns exist"
+        );
         for (i, col) in cols_data.iter().enumerate().skip(1) {
             assert!(
                 col.len() == rows,
@@ -32,8 +36,14 @@ impl<T: Clone> Matrix<T> {
     }
 
     pub fn from_vec(data: Vec<T>, rows: usize, cols: usize) -> Self {
-        assert!(rows > 0, "need at least one row");
-        assert!(cols > 0, "need at least one column");
+        assert!(
+            rows > 0 || cols == 0,
+            "need at least one row if columns exist"
+        );
+        assert!(
+            cols > 0 || rows == 0,
+            "need at least one column if rows exist"
+        );
         assert_eq!(data.len(), rows * cols, "data length mismatch");
         Matrix { rows, cols, data }
     }
@@ -67,11 +77,23 @@ impl<T: Clone> Matrix<T> {
 
     #[inline]
     pub fn column(&self, c: usize) -> &[T] {
+        assert!(
+            c < self.cols,
+            "column index {} out of bounds for {} columns",
+            c,
+            self.cols
+        );
         let start = c * self.rows;
         &self.data[start..start + self.rows]
     }
     #[inline]
     pub fn column_mut(&mut self, c: usize) -> &mut [T] {
+        assert!(
+            c < self.cols,
+            "column index {} out of bounds for {} columns",
+            c,
+            self.cols
+        );
         let start = c * self.rows;
         &mut self.data[start..start + self.rows]
     }
@@ -90,8 +112,16 @@ impl<T: Clone> Matrix<T> {
     /// Swaps two columns in the matrix.
     pub fn swap_columns(&mut self, c1: usize, c2: usize) {
         assert!(
-            c1 < self.cols && c2 < self.cols,
-            "column index out of bounds"
+            c1 < self.cols,
+            "column index c1={} out of bounds for {} columns",
+            c1,
+            self.cols
+        );
+        assert!(
+            c2 < self.cols,
+            "column index c2={} out of bounds for {} columns",
+            c2,
+            self.cols
         );
         if c1 == c2 {
             // Indices are equal; no operation required
@@ -132,7 +162,7 @@ impl<T: Clone> Matrix<T> {
 impl<T: Clone> Matrix<T> {
     /// Adds a column to the matrix at the specified index.
     pub fn add_column(&mut self, index: usize, column: Vec<T>) {
-        assert!(index <= self.cols, "column index out of bounds");
+        assert!(index <= self.cols, "add_column index {} out of bounds for {} columns", index, self.cols);
         assert_eq!(column.len(), self.rows, "column length mismatch");
 
         for (r, value) in column.into_iter().enumerate() {
@@ -143,7 +173,7 @@ impl<T: Clone> Matrix<T> {
 
     /// Adds a row to the matrix at the specified index.
     pub fn add_row(&mut self, index: usize, row: Vec<T>) {
-        assert!(index <= self.rows, "row index out of bounds");
+        assert!(index <= self.rows, "add_row index {} out of bounds for {} rows", index, self.rows);
         assert_eq!(row.len(), self.cols, "row length mismatch");
 
         for (c, value) in row.into_iter().enumerate() {
@@ -159,7 +189,14 @@ impl<T> Index<(usize, usize)> for Matrix<T> {
     #[inline]
     fn index(&self, (r, c): (usize, usize)) -> &T {
         // Validate that the requested indices are within bounds
-        assert!(r < self.rows && c < self.cols, "index out of bounds");
+        assert!(
+            r < self.rows && c < self.cols,
+            "index out of bounds: ({}, {}) vs {}x{}",
+            r,
+            c,
+            self.rows,
+            self.cols
+        );
         // Compute column-major offset and return reference
         &self.data[c * self.rows + r]
     }
@@ -169,7 +206,14 @@ impl<T> IndexMut<(usize, usize)> for Matrix<T> {
     #[inline]
     fn index_mut(&mut self, (r, c): (usize, usize)) -> &mut T {
         // Validate that the requested indices are within bounds
-        assert!(r < self.rows && c < self.cols, "index out of bounds");
+        assert!(
+            r < self.rows && c < self.cols,
+            "index out of bounds: ({}, {}) vs {}x{}",
+            r,
+            c,
+            self.rows,
+            self.cols
+        );
         // Compute column-major offset and return mutable reference
         &mut self.data[c * self.rows + r]
     }