From a64c9f1e7cc9616c54296ca3983123e15ec486f1 Mon Sep 17 00:00:00 2001
From: Tianyi Zheng <tianyizheng02@gmail.com>
Date: Sun, 31 Oct 2021 14:16:02 +0000
Subject: [PATCH] Deduplicate euclidean_length method in Vector (#5658)

* Rewrite parts of Vector and Matrix methods

* Refactor determinant method and add unit tests

Refactor determinant method to create separate minor and cofactor
methods.
Add respective unit tests for new methods.
Rename methods using snake case to follow Python naming conventions.

* Reorganize Vector and Matrix methods

* Update linear_algebra/README.md

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Fix punctuation and wording

* Apply suggestions from code review

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Deduplicate euclidean length method for Vector

* Add more unit tests for Euclidean length method

* Fix bug in unit test for euclidean_length

* Remove old comments for magnitude method

Co-authored-by: John Law <johnlaw.po@gmail.com>
---
 linear_algebra/src/lib.py                 | 33 +++++++++++------------
 linear_algebra/src/test_linear_algebra.py |  8 +++++-
 2 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/linear_algebra/src/lib.py b/linear_algebra/src/lib.py
index dad0a8c0a..85dc4b71c 100644
--- a/linear_algebra/src/lib.py
+++ b/linear_algebra/src/lib.py
@@ -44,7 +44,6 @@ class Vector:
         component(i): gets the i-th component (0-indexed)
         change_component(pos: int, value: float): changes specified component
         euclidean_length(): returns the euclidean length of the vector
-        magnitude(): returns the magnitude of the vector
         angle(other: Vector, deg: bool): returns the angle between two vectors
         TODO: compare-operator
     """
@@ -159,18 +158,20 @@ class Vector:
     def euclidean_length(self) -> float:
         """
         returns the euclidean length of the vector
-        """
-        squares = [c ** 2 for c in self.__components]
-        return math.sqrt(sum(squares))
 
-    def magnitude(self) -> float:
-        """
-        Magnitude of a Vector
-
-        >>> Vector([2, 3, 4]).magnitude()
+        >>> Vector([2, 3, 4]).euclidean_length()
         5.385164807134504
-
+        >>> Vector([1]).euclidean_length()
+        1.0
+        >>> Vector([0, -1, -2, -3, 4, 5, 6]).euclidean_length()
+        9.539392014169456
+        >>> Vector([]).euclidean_length()
+        Traceback (most recent call last):
+        ...
+        Exception: Vector is empty
         """
+        if len(self.__components) == 0:
+            raise Exception("Vector is empty")
         squares = [c ** 2 for c in self.__components]
         return math.sqrt(sum(squares))
 
@@ -188,7 +189,7 @@ class Vector:
         Exception: invalid operand!
         """
         num = self * other
-        den = self.magnitude() * other.magnitude()
+        den = self.euclidean_length() * other.euclidean_length()
         if deg:
             return math.degrees(math.acos(num / den))
         else:
@@ -267,8 +268,7 @@ class Matrix:
 
     def __init__(self, matrix: list[list[float]], w: int, h: int) -> None:
         """
-        simple constructor for initializing
-        the matrix with components.
+        simple constructor for initializing the matrix with components.
         """
         self.__matrix = matrix
         self.__width = w
@@ -276,8 +276,7 @@ class Matrix:
 
     def __str__(self) -> str:
         """
-        returns a string representation of this
-        matrix.
+        returns a string representation of this matrix.
         """
         ans = ""
         for i in range(self.__height):
@@ -291,7 +290,7 @@ class Matrix:
 
     def __add__(self, other: Matrix) -> Matrix:
         """
-        implements the matrix-addition.
+        implements matrix addition.
         """
         if self.__width == other.width() and self.__height == other.height():
             matrix = []
@@ -307,7 +306,7 @@ class Matrix:
 
     def __sub__(self, other: Matrix) -> Matrix:
         """
-        implements the matrix-subtraction.
+        implements matrix subtraction.
         """
         if self.__width == other.width() and self.__height == other.height():
             matrix = []
diff --git a/linear_algebra/src/test_linear_algebra.py b/linear_algebra/src/test_linear_algebra.py
index de7041a17..724ceef25 100644
--- a/linear_algebra/src/test_linear_algebra.py
+++ b/linear_algebra/src/test_linear_algebra.py
@@ -42,12 +42,18 @@ class Test(unittest.TestCase):
         x = Vector([1, 2, 3, 4])
         self.assertEqual(len(x), 4)
 
-    def test_euclidLength(self) -> None:
+    def test_euclidean_length(self) -> None:
         """
         test for method euclidean_length()
         """
         x = Vector([1, 2])
+        y = Vector([1, 2, 3, 4, 5])
+        z = Vector([0, 0, 0, 0, 0, 0, 0, 0, 0, 0])
+        w = Vector([1, -1, 1, -1, 2, -3, 4, -5])
         self.assertAlmostEqual(x.euclidean_length(), 2.236, 3)
+        self.assertAlmostEqual(y.euclidean_length(), 7.416, 3)
+        self.assertEqual(z.euclidean_length(), 0)
+        self.assertAlmostEqual(w.euclidean_length(), 7.616, 3)
 
     def test_add(self) -> None:
         """