in_static_equilibrium checks if a 2D static system is in equilibrium (#1062)

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arithmetic_analysis/in_static_equilibrium.py

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+"""
+Checks if a system of forces is in static equilibrium.
+
+python/black : true
+flake8 : passed
+mypy : passed
+"""
+
+from numpy import array, cos, sin, radians, cross  # type: ignore
+from typing import List
+
+
+def polar_force(
+    magnitude: float, angle: float, radian_mode: bool = False
+) -> List[float]:
+    """
+    Resolves force along rectangular components.
+    (force, angle) => (force_x, force_y)
+    >>> polar_force(10, 45)
+    [7.0710678118654755, 7.071067811865475]
+    >>> polar_force(10, 3.14, radian_mode=True)
+    [-9.999987317275394, 0.01592652916486828]
+    """
+    if radian_mode:
+        return [magnitude * cos(angle), magnitude * sin(angle)]
+    return [magnitude * cos(radians(angle)), magnitude * sin(radians(angle))]
+
+
+def in_static_equilibrium(
+    forces: array, location: array, eps: float = 10 ** -1
+) -> bool:
+    """
+    Check if a system is in equilibrium.
+    It takes two numpy.array objects.
+    forces ==>  [
+                        [force1_x, force1_y],
+                        [force2_x, force2_y],
+                        ....]
+    location ==>  [
+                        [x1, y1],
+                        [x2, y2],
+                        ....]
+    >>> force = array([[1, 1], [-1, 2]])
+    >>> location = array([[1, 0], [10, 0]])
+    >>> in_static_equilibrium(force, location)
+    False
+    """
+    # summation of moments is zero
+    moments: array = cross(location, forces)
+    sum_moments: float = sum(moments)
+    return abs(sum_moments) < eps
+
+
+if __name__ == "__main__":
+    # Test to check if it works
+    forces = array(
+        [
+            polar_force(718.4, 180 - 30),
+            polar_force(879.54, 45),
+            polar_force(100, -90)
+        ])
+
+    location = array([[0, 0], [0, 0], [0, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    # Problem 1 in image_data/2D_problems.jpg
+    forces = array(
+        [
+            polar_force(30 * 9.81, 15),
+            polar_force(215, 180 - 45),
+            polar_force(264, 90 - 30),
+        ]
+    )
+
+    location = array([[0, 0], [0, 0], [0, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    # Problem in image_data/2D_problems_1.jpg
+    forces = array([[0, -2000], [0, -1200], [0, 15600], [0, -12400]])
+
+    location = array([[0, 0], [6, 0], [10, 0], [12, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    import doctest
+
+    doctest.testmod()