code: def _generic_dispersion_derivative(
      tr,
      oversampling=50,
      time_length=32.0,
      onset=0.0,
      undershoot=16,
      ratio=0.167,
      dispersion=1.0,
      dt=0.01,
  ):
      """Return the dispersion derivative of an hrf.
  
      Parameters
      ----------
      dt : float, default=0.01
          Dispersion step for the derivative.
  
      See _gamma_difference_hrf for the other parameters description.
      """
      return _compute_derivative_from_values(
          _gamma_difference_hrf(
              tr,
              oversampling,
              time_length,
              onset,
              undershoot=undershoot,
              ratio=ratio,
              dispersion=dispersion,
          ),
          _gamma_difference_hrf(
              tr,
              oversampling,
              time_length,
              onset,
              undershoot=undershoot,
              ratio=ratio,
              dispersion=dispersion + dt,
          ),
          dt=dt,
      )
  
imports: import warnings
  from collections.abc import Iterable
  import numpy
  from scipy.stats import gamma
  from nilearn._utils import fill_doc
label_desc: Use image node_id 8 for calling a global function with example usage: _generic_dispersion_derivative(tr, oversampling, time_length, onset, undershoot, ratio, dispersion, dt) and returns: _compute_derivative_from_values