code: def gaussian_kernel(X, beta, Y=None):
      if Y is None:
          Y = X
      diff = X[:, None, :] - Y[None, :, :]
      diff = np.square(diff)
      diff = np.sum(diff, 2)
      return np.exp(-diff / (2 * beta**2))
  
file_path: dipy/dipy/align/cpd.py
imports: import numpy
  import numbers
  from warnings import warn
label_desc: Use image node_id 1 for calling a global function with example usage: gaussian_kernel(X, beta, Y) and returns: np