[mypy] Fix directory arithmetic_analysis (#4304)

* fix directory arithmetic_analysis

* Update build.yml

* temporary fix for psf/black bug

see https://github.com/psf/black/issues/2079

* Update in_static_equilibrium.py

.github/workflows/build.yml

@@ -23,7 +23,7 @@ jobs:
           python -m pip install mypy pytest-cov -r requirements.txt
       # FIXME: #4052 fix mypy errors in the exclude directories and remove them below
       - run: mypy --ignore-missing-imports
-          --exclude '(arithmetic_analysis|ciphers|conversions|data_structures|digital_image_processing|dynamic_programming|graphs|hashes|linear_algebra|maths|matrix|other|project_euler|scripts|searches|strings*)/$' .
+          --exclude '(ciphers|conversions|data_structures|digital_image_processing|dynamic_programming|graphs|hashes|linear_algebra|maths|matrix|other|project_euler|scripts|searches|strings*)/$' .
       - name: Run tests
         run: pytest --doctest-modules --ignore=project_euler/ --ignore=scripts/ --cov-report=term-missing:skip-covered --cov=. .
       - if: ${{ success() }}

.github/workflows/pre-commit.yml

@@ -14,7 +14,7 @@ jobs:
             ~/.cache/pip
           key: ${{ runner.os }}-pre-commit-${{ hashFiles('.pre-commit-config.yaml') }}
       - uses: actions/setup-python@v2
-      - uses: psf/black@stable
+      - uses: psf/black@20.8b1
       - name: Install pre-commit
         run: |
           python -m pip install --upgrade pip

arithmetic_analysis/gaussian_elimination.py

@@ -7,7 +7,7 @@ Gaussian elimination - https://en.wikipedia.org/wiki/Gaussian_elimination
 import numpy as np
 
 
-def retroactive_resolution(coefficients: np.matrix, vector: np.array) -> np.array:
+def retroactive_resolution(coefficients: np.matrix, vector: np.ndarray) -> np.ndarray:
     """
     This function performs a retroactive linear system resolution
         for triangular matrix
@@ -38,7 +38,7 @@ def retroactive_resolution(coefficients: np.matrix, vector: np.array) -> np.arra
     return x
 
 
-def gaussian_elimination(coefficients: np.matrix, vector: np.array) -> np.array:
+def gaussian_elimination(coefficients: np.matrix, vector: np.ndarray) -> np.ndarray:
     """
     This function performs Gaussian elimination method
 
@@ -57,7 +57,7 @@ def gaussian_elimination(coefficients: np.matrix, vector: np.array) -> np.array:
     # coefficients must to be a square matrix so we need to check first
     rows, columns = np.shape(coefficients)
     if rows != columns:
-        return []
+        return np.array((), dtype=float)
 
     # augmented matrix
     augmented_mat = np.concatenate((coefficients, vector), axis=1)

arithmetic_analysis/in_static_equilibrium.py

@@ -3,7 +3,7 @@ Checks if a system of forces is in static equilibrium.
 """
 from typing import List
 
-from numpy import array, cos, cross, radians, sin
+from numpy import array, cos, cross, ndarray, radians, sin
 
 
 def polar_force(
@@ -23,7 +23,7 @@ def polar_force(
 
 
 def in_static_equilibrium(
-    forces: array, location: array, eps: float = 10 ** -1
+    forces: ndarray, location: ndarray, eps: float = 10 ** -1
 ) -> bool:
     """
     Check if a system is in equilibrium.
@@ -42,7 +42,7 @@ def in_static_equilibrium(
     False
     """
     # summation of moments is zero
-    moments: array = cross(location, forces)
+    moments: ndarray = cross(location, forces)
     sum_moments: float = sum(moments)
     return abs(sum_moments) < eps