code: def test_parameters_eval(parameters):
      """Test the eval method."""
      pars, _, _ = parameters
      evaluated = pars.eval("10.0*a+b")
      assert_allclose(evaluated, 120)
  
      # check that eval() works with usersyms and parameter values
      def myfun(x):
          return 2.0 * x
  
      pars2 = lmfit.Parameters(usersyms={"myfun": myfun})
      pars2.add("a", value=4.0)
      pars2.add("b", value=3.0)
      assert_allclose(pars2.eval("myfun(2.0) * a"), 16)
      assert_allclose(pars2.eval("b / myfun(3.0)"), 0.5)
  
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 17 for calling a global function with example usage: test_parameters_eval(parameters) and returns: unknown