code: def test_parameters_usersyms():
      """Test for passing usersyms to Parameters()."""
  
      def myfun(x):
          return x**3
  
      params = lmfit.Parameters(usersyms={"myfun": myfun})
      params.add("a", value=2.3)
      params.add("b", expr="myfun(a)")
  
      np.random.seed(2020)
      xx = np.linspace(0, 1, 10)
      yy = 3 * xx + np.random.normal(scale=0.002, size=xx.size)
  
      model = lmfit.Model(lambda x, a: a * x)
      result = model.fit(yy, params=params, x=xx)
      assert_allclose(result.params["a"].value, 3.0, rtol=1e-3)
      assert result.nfev > 3 and result.nfev < 300
  
imports: from copy import copy, deepcopy
  import os
  import pickle
  import numpy
  from numpy.testing import assert_allclose
  import pytest
  import lmfit
  from lmfit.models import VoigtModel
label_desc: Use image node_id 29 for calling a global function with example usage: test_parameters_usersyms() and returns: unknown