code: def _basic_delta(iso, m, n, theta, phi):
      """Simple delta function
      Parameters
      ----------
      iso: int
          Number of tissue compartments for running the MSMT-CSD. Minimum
          number of compartments required is 2.
          Default: 2
      m : int ``|m| <= n``
          The order of the harmonic.
      n : int ``>= 0``
          The degree of the harmonic.
      theta : array_like
         inclination or polar angle
      phi : array_like
         azimuth angle
      """
      wm_d = shm.gen_dirac(m, n, theta, phi)
      iso_d = [SH_CONST] * iso
      return np.concatenate([iso_d, wm_d])
  
imports: from packaging.version import Version
  import numbers
  import warnings
  import numpy
  from dipy.core import geometry
  from dipy.core.gradients import GradientTable, gradient_table, unique_bvals_tolerance, get_bval_indices
  from dipy.data import default_sphere
  from dipy.reconst import shm
  from dipy.reconst.csdeconv import response_from_mask_ssst
  from dipy.reconst.dti import TensorModel, fractional_anisotropy, mean_diffusivity
  from dipy.reconst.multi_voxel import multi_voxel_fit
  from dipy.reconst.utils import _roi_in_volume, _mask_from_roi
  from dipy.sims.voxel import single_tensor
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 3 for calling a global function with example usage: _basic_delta(iso, m, n, theta, phi) and returns: np