code: def solid_angle(center, coords):
      
      o = np.array(center)
      r = [np.array(c) - o for c in coords]
      r.append(r[0])
      n = [np.cross(r[i + 1], r[i]) for i in range(len(r) - 1)]
      n.append(np.cross(r[1], r[0]))
      vals = []
      for i in range(len(n) - 1):
          v = -np.dot(n[i], n[i + 1]) \
              / (np.linalg.norm(n[i]) * np.linalg.norm(n[i + 1]))
          vals.append(acos(abs_cap(v)))
      phi = sum(vals)
      return phi + (3 - len(r)) * pi
docs: Helper method to calculate the solid angle of a set of coords from the
      center.
  
      Args:
          center (3x1 array): Center to measure solid angle from.
          coords (Nx3 array): List of coords to determine solid angle.
  
      Returns:
          The solid angle.