code: def backward(self):
      self.a_sqrt = np.reshape(self.a_sqrt, self.a_sqrt.shape + (1,))
      self.b_sqrt = np.reshape(self.b_sqrt, self.b_sqrt.shape + (1,))
      self.sim = np.reshape(self.sim, self.sim.shape + (1,))
      ga = self.b / (
          self.a_sqrt * self.b_sqrt
      ) - self.sim * self.a / np.square(self.a_sqrt)
      gb = self.a / (
          self.a_sqrt * self.b_sqrt
      ) - self.sim * self.b / np.square(self.b_sqrt)
      return {"a": ga, "b": gb}
  
file_path: CNTK/bindings/python/cntk/losses/tests/cosine_distance_test.py
imports: import numpy
  import pytest
  import cntk
label_desc: Use image node_id 3 for calling the numpy_cos obj's underlying member method code with example usage: obj.backward() and returns: dict