Add broadcasting functionality for 1-row matrices with tests

src/matrix/mat.rs

@@ -383,6 +383,25 @@ impl<T: Clone> Matrix<T> {
             data: vec![value; rows * cols], // Fill with the specified value
         }
     }
+
+    /// Creates a new matrix by broadcasting a 1-row matrix to a target shape.
+    /// Panics if `self` is not a 1-row matrix or if `self.cols()` does not match `target_cols`.
+    pub fn broadcast_row_to_target_shape(&self, target_rows: usize, target_cols: usize) -> Matrix<T> {
+        assert_eq!(self.rows(), 1, "broadcast_row_to_target_shape can only be called on a 1-row matrix.");
+        assert_eq!(self.cols(), target_cols, "Column count mismatch for broadcasting: source has {} columns, target has {} columns.", self.cols(), target_cols);
+
+        let mut data = Vec::with_capacity(target_rows * target_cols);
+        let original_row_data = self.row(0); // Get the single row data
+
+        for _ in 0..target_rows { // Repeat 'target_rows' times
+            for value in &original_row_data { // Iterate over elements of the row
+                data.push(value.clone());
+            }
+        }
+        // The data is now in row-major order for the new matrix.
+        // We need to convert it to column-major for Matrix::from_vec.
+        Matrix::from_rows_vec(data, target_rows, target_cols)
+    }
 }
 
 impl Matrix<f64> {
@@ -1992,4 +2011,47 @@ mod tests {
             assert!(value.is_nan(), "Expected NaN, got {}", value);
         }
     }
+
+    #[test]
+    fn test_broadcast_row_to_target_shape_basic() {
+        let single_row_matrix = Matrix::from_rows_vec(vec![1.0, 2.0, 3.0], 1, 3);
+        let target_rows = 5;
+        let target_cols = 3;
+
+        let broadcasted = single_row_matrix.broadcast_row_to_target_shape(target_rows, target_cols);
+
+        assert_eq!(broadcasted.rows(), target_rows);
+        assert_eq!(broadcasted.cols(), target_cols);
+
+        for r in 0..target_rows {
+            assert_eq!(broadcasted.row(r), vec![1.0, 2.0, 3.0]);
+        }
+    }
+
+    #[test]
+    fn test_broadcast_row_to_target_shape_single_row() {
+        let single_row_matrix = Matrix::from_rows_vec(vec![10.0, 20.0], 1, 2);
+        let target_rows = 1;
+        let target_cols = 2;
+
+        let broadcasted = single_row_matrix.broadcast_row_to_target_shape(target_rows, target_cols);
+
+        assert_eq!(broadcasted.rows(), target_rows);
+        assert_eq!(broadcasted.cols(), target_cols);
+        assert_eq!(broadcasted.row(0), vec![10.0, 20.0]);
+    }
+
+    #[test]
+    #[should_panic(expected = "broadcast_row_to_target_shape can only be called on a 1-row matrix.")]
+    fn test_broadcast_row_to_target_shape_panic_not_1_row() {
+        let multi_row_matrix = Matrix::from_rows_vec(vec![1.0, 2.0, 3.0, 4.0], 2, 2);
+        multi_row_matrix.broadcast_row_to_target_shape(3, 2);
+    }
+
+    #[test]
+    #[should_panic(expected = "Column count mismatch for broadcasting: source has 3 columns, target has 4 columns.")]
+    fn test_broadcast_row_to_target_shape_panic_col_mismatch() {
+        let single_row_matrix = Matrix::from_rows_vec(vec![1.0, 2.0, 3.0], 1, 3);
+        single_row_matrix.broadcast_row_to_target_shape(5, 4);
+    }
 }