code: def Matern32(ls, x1, x2=None, grad=False):
      r = np.sqrt(dist2(ls, x1, x2))
      cov = (1 + SQRT_3 * r) * np.exp(-SQRT_3 * r)
      if grad:
          return (cov, grad_Matern32(ls, x1, x2))
      else:
          return cov
  
file_path: auptimizer/src/aup/Proposer/spearmint/gp.py
imports: import numpy
  import scipy.linalg
  import scipy.optimize
  import scipy.io
label_desc: Use image node_id 6 for calling a global function with example usage: Matern32(ls, x1, x2, grad) and returns: cov,  grad_Matern32, cov