code: def test_uvars_calc_afterfit():
      """test using uvars by hand"""
      pars = nist_model.make_params(
          g1_center=110,
          g1_amplitude=4000,
          g1_sigma=25,
          g2_center=160,
          g2_amplitude=2000,
          g2_sigma=20,
          exp_amplitude=50,
          exp_decay=75,
      )
  
      out = nist_model.fit(y, pars, x=x)
  
      assert out.nfev > 25
      assert out.errorbars
      assert out.chisqr > 1000
      assert out.chisqr < 3000
  
      u_g1amp = out.uvars["g1_amplitude"]
      u_g2amp = out.uvars["g2_amplitude"]
  
      # stderr in area of Gauss1 + Gauss2 in quadrature, ignoring correlations
      area_stderr_quad = np.sqrt(
          out.params["g1_amplitude"].stderr ** 2
          + out.params["g2_amplitude"].stderr ** 2
      )
      assert area_stderr_quad > 53
      assert area_stderr_quad < 58
  
      # stderr in area of Gauss1 + Gauss2 including correlations: smaller.
      area_stderr_uvars = (u_g1amp + u_g2amp).std_dev
      assert area_stderr_uvars > 43
      assert area_stderr_uvars < 48
  
file_path: lmfit-py/tests/test_params_uvars.py
imports: import os
  import numpy
  from lmfit import create_params, minimize
  from lmfit.models import ExponentialModel, GaussianModel
label_desc: Use image node_id 1 for calling a global function with example usage: test_uvars_calc_afterfit() without return types