docstr: Cost function for differential evolution algorithm. Performs a
  stochastic search for the non-linear parameters 'x'. The objective
  function is calculated in the :func: `ivim_mix_cost_one`. The function
  constructs the parameters using :func: `phi`.
  
  Parameters
  ----------
  x : array
      input from the Differential Evolution optimizer.
  
  signal : array
      The signal values measured for this model.
  
  Returns
  -------
  :func: `ivim_mix_cost_one`
code: def stoc_search_cost(self, x, signal):
      """
      Cost function for differential evolution algorithm. Performs a
      stochastic search for the non-linear parameters 'x'. The objective
      function is calculated in the :func: `ivim_mix_cost_one`. The function
      constructs the parameters using :func: `phi`.
  
      Parameters
      ----------
      x : array
          input from the Differential Evolution optimizer.
  
      signal : array
          The signal values measured for this model.
  
      Returns
      -------
      :func: `ivim_mix_cost_one`
  
      """
      phi = self.phi(x)
      return self.ivim_mix_cost_one(phi, signal)
  
imports: import warnings
  import numpy
  from scipy.optimize import least_squares, differential_evolution
  from dipy.reconst.base import ReconstModel
  from dipy.reconst.multi_voxel import multi_voxel_fit
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 3 for calling the IvimModelVP obj's underlying member method code with example usage: obj.stoc_search_cost(x, signal) and returns: self