Added documentation entry for NumPy ndarray trace() method

content/numpy/concepts/ndarray/terms/trace/trace.md

@@ -0,0 +1,89 @@
+---
+Title: '.trace()'
+Description: 'Returns the sum of the elements along the diagonal of an array.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Arrays'
+  - 'Linear Algebra'
+  - 'Matrices'
+  - 'NumPy'
+  - 'Python'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/data-science'
+---
+
+The **`.trace()`** method returns the sum of the elements along the diagonal of a [NumPy](https://www.codecademy.com/resources/docs/numpy) array. For 2D arrays, the diagonal consists of elements where the row index equals the column index. For multi-dimensional arrays, the axes specified by axis1 and axis2 define the matrix dimensions for diagonal summation.
+
+The `.trace()` method supports optional parameters to select a diagonal offset or specify axes, making it versatile for arrays of different shapes and orientations.
+
+## Syntax
+
+```pseudo
+ndarray.trace(offset=0, axis1=0, axis2=1, dtype=None, out=None)
+```
+
+**Parameters:**
+
+- `offset` (Optional): The diagonal offset from the main diagonal. A positive value selects a diagonal above the main diagonal, while a negative value selects one below. Default is `0` (main diagonal).
+- `axis1` (Optional): The axis to be used as the first axis of the 2D sub-arrays from which the diagonals should be taken. Default is `0`.
+- `axis2` (Optional): The axis to be used as the second axis of the 2D sub-arrays from which the diagonals should be taken. Default is `1`.
+- `dtype` (Optional): The data type of the returned array. If not specified, it is determined from the input array.
+- `out` (Optional): An alternative output array to place the result. It must have the same shape as the expected output.
+
+**Return value:**
+
+Returns the sum of the diagonal elements as a scalar or array, depending on the input array's dimensions and the specified parameters.
+
+## Example
+
+This example demonstrates how to use `.trace()` to calculate the sum of the main diagonal elements of a 2D array:
+
+```py
+import numpy as np
+
+# Create a 2D array
+array_2d = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
+print("Original array:")
+print(array_2d)
+
+# Calculate the trace (sum of main diagonal)
+trace_value = array_2d.trace()
+print("\nTrace (sum of diagonal elements):", trace_value)
+```
+
+The output produced by this code is:
+
+```shell
+Original array:
+[[1 2 3]
+ [4 5 6]
+ [7 8 9]]
+
+Trace (sum of diagonal elements): 15
+```
+
+This code creates a 3×3 array and calculates the trace by summing the diagonal elements (1 + 5 + 9 = 15).
+
+## Codebyte Example
+
+```codebyte/python
+import numpy as np
+
+# Create a 3x3 matrix
+matrix = np.array([[2, 0, 1], [1, 1, 0], [0, 1, 2]])
+print("Matrix:")
+print(matrix)
+
+# Calculate the trace
+trace_result = matrix.trace()
+print("\nTrace of the matrix:", trace_result)
+
+# Calculate trace with offset
+trace_offset_1 = matrix.trace(offset=1)
+trace_offset_minus_1 = matrix.trace(offset=-1)
+print("Trace with offset 1 (above diagonal):", trace_offset_1)
+print("Trace with offset -1 (below diagonal):", trace_offset_minus_1)
+```