code: def gaussian_parallel(q, tau, D=0.7e-3):
      r"""Calculates the parallel Gaussian diffusion signal.
  
      Parameters
      ----------
      q : array, shape (N,)
          q-space value in 1/mm
      tau : float
          diffusion time in s
      D : float, optional
          diffusion constant
  
      Returns
      -------
      E : array, shape (N,)
          signal attenuation
  
      """
      return np.exp(-((2 * np.pi * q) ** 2) * tau * D)
  
imports: import numpy
  from numpy import dot
  from dipy.core.geometry import sphere2cart
  from dipy.core.geometry import vec2vec_rotmat
  from dipy.core.gradients import GradientTable
  from dipy.reconst.utils import dki_design_matrix
  from scipy.special import jn
label_desc: Use image node_id 8 for calling a global function with example usage: gaussian_parallel(q, tau, D) and returns: np