diff --git a/src/frame/ops.rs b/src/frame/ops.rs
index f52ee9d..c35625e 100644
--- a/src/frame/ops.rs
+++ b/src/frame/ops.rs
@@ -96,9 +96,10 @@ impl BoolOps for Frame<bool> {
 //     }
 // }
 
+#[cfg(test)]
 mod tests {
-    use crate::frame::*;
-    use crate::matrix::*;
+    use super::*;
+    use crate::matrix::Matrix;
 
     #[test]
     fn test_series_ops() {
diff --git a/src/matrix/mat.rs b/src/matrix/mat.rs
index b3d93b6..4798ccd 100644
--- a/src/matrix/mat.rs
+++ b/src/matrix/mat.rs
@@ -1,4 +1,6 @@
-use std::ops::{Index, IndexMut, Not};
+//! A simple column-major Matrix implementation with element-wise operations.
+
+use std::ops::{Add, BitAnd, BitOr, BitXor, Div, Index, IndexMut, Mul, Not, Sub};
 
 /// A column‑major 2D matrix of `T`
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -13,9 +15,15 @@ impl<T: Clone> Matrix<T> {
     pub fn from_cols(cols_data: Vec<Vec<T>>) -> Self {
         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");
-        for (i, col) in cols_data.iter().enumerate().skip(1) {
+        // Handle empty cols_data
+        let rows = cols_data.get(0).map_or(0, |c| c.len());
+        // 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() {
             assert!(
                 col.len() == rows,
                 "col {} has len {}, expected {}",
@@ -24,17 +32,34 @@ impl<T: Clone> Matrix<T> {
                 rows
             );
         }
-        let mut data = Vec::with_capacity(rows * cols);
-        for col in cols_data {
-            data.extend(col);
-        }
+        // Flatten column data directly
+        let data = cols_data.into_iter().flatten().collect();
         Matrix { rows, cols, data }
     }
 
+    /// Build from a flat Vec, assuming column-major order.
     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_eq!(data.len(), rows * cols, "data length mismatch");
+        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"
+        );
+        if rows * cols != 0 {
+            // Only assert length if matrix is non-empty
+            assert_eq!(
+                data.len(),
+                rows * cols,
+                "data length mismatch: expected {}, got {}",
+                rows * cols,
+                data.len()
+            );
+        } else {
+            assert!(data.is_empty(), "data must be empty for 0-sized matrix");
+        }
+
         Matrix { rows, cols, data }
     }
 
@@ -46,7 +71,13 @@ impl<T: Clone> Matrix<T> {
         &mut self.data
     }
 
-    pub fn as_vec(&self) -> Vec<T> {
+    /// Consumes the Matrix and returns its underlying data Vec.
+    pub fn into_vec(self) -> Vec<T> {
+        self.data
+    }
+
+    /// Creates a new Vec<T> containing the matrix data (cloned).
+    pub fn to_vec(&self) -> Vec<T> {
         self.data.clone()
     }
 
@@ -58,20 +89,36 @@ impl<T: Clone> Matrix<T> {
         self.cols
     }
 
+    /// Get element reference (immutable). Panics on out-of-bounds.
     pub fn get(&self, r: usize, c: usize) -> &T {
         &self[(r, c)]
     }
+
+    /// Get element reference (mutable). Panics on out-of-bounds.
     pub fn get_mut(&mut self, r: usize, c: usize) -> &mut T {
         &mut self[(r, c)]
     }
 
     #[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]
     }
@@ -87,11 +134,19 @@ impl<T: Clone> Matrix<T> {
         })
     }
 
-    /// Swaps two columns in the matrix.
+    /// Swaps two columns in the matrix. Panics on out-of-bounds.
     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 +187,7 @@ 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() {
@@ -143,8 +198,8 @@ 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_eq!(row.len(), self.cols, "row length mismatch");
+        assert!(index <= self.rows,"add_row index {} out of bounds for {} rows",index,self.rows);
+        assert_eq!(row.len(),self.cols,"row length mismatch: expected {} (cols), got {}",self.cols,row.len());
 
         for (c, value) in row.into_iter().enumerate() {
             self.data.insert(c * (self.rows + 1) + index, value);
@@ -159,7 +214,14 @@ 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 +231,14 @@ 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]
     }
@@ -196,14 +265,16 @@ impl<'a, T> MatrixRow<'a, T> {
 /// Specifies the axis along which to perform a reduction operation.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Axis {
-    /// Apply reduction along columns (vertical axis).
+    /// Apply reduction along columns (vertical axis). Result has 1 row.
     Col,
-    /// Apply reduction along rows (horizontal axis).
+    /// Apply reduction along rows (horizontal axis). Result has 1 column.
     Row,
 }
 
+// --- Broadcasting ---
+
 /// A trait to turn either a `Matrix<T>` or a scalar T into a `Vec<T>` of
-/// length `rows*cols` (broadcasting the scalar).
+/// length `rows*cols` (broadcasting the scalar). Used for comparisons.
 pub trait Broadcastable<T> {
     fn to_vec(&self, rows: usize, cols: usize) -> Vec<T>;
 }