title: Uncertainties on fitted parameters in lmfit
body: <p>I'm looking for the easiest way of outputting the uncertainty in the fitted parameters. With spo.curve_fit, we just get the covariance matrix when we fit and we can take the diagonal and square root to find the uncertainties. With lmfit it doesn't seem to be so simple.</p>
  
  <p>My fitting looks like this:</p>
  
  <pre><code>import lmfit 
  
  
  a_lm2 = lmfit.Parameter('a', value=a_est)
  b_lm2 = lmfit.Parameter('b', value=b_est)
  x0_core_lm2 = lmfit.Parameter('x0_core', value=gaus1['x0_core'])
  x0_1_lm2 = lmfit.Parameter('x0_1', value=gaus1['x0_1'])
  x0_2_lm2 = lmfit.Parameter('x0_2', value=gaus1['x0_2'])
  x0_3_lm2 = lmfit.Parameter('x0_3', value=gaus1['x0_3'])
  x0_4_lm2 = lmfit.Parameter('x0_4', value=gaus1['x0_4'])
  sig_core_lm2 = lmfit.Parameter('sig_core', value=gaus1['sig_core'])
  sig_1_lm2 = lmfit.Parameter('sig_1', value=gaus1['sig_1'])
  sig_2_lm2 = lmfit.Parameter('sig_2', value=gaus1['sig_2'])
  sig_3_lm2 = lmfit.Parameter('sig_3', value=gaus1['sig_3'])
  sig_4_lm2 = lmfit.Parameter('sig_4', value=gaus1['sig_4'])
  m_lm2 = lmfit.Parameter('m', value=m, vary=False)
  c_lm2 = lmfit.Parameter('c', value=c, vary=False)
  
  
  gausfit2 = mod.fit(y, x=x, a=a_lm2, b=b_lm2, x0_core=x0_core_lm2, x0_1=x0_1_lm2, x0_2=x0_2_lm2,
  
  x0_3=x0_3_lm2, x0_4=x0_4_lm2, sig_core=sig_core_lm2, sig_1=sig_1_lm2, sig_2=sig_2_lm2,
  
  sig_3=sig_3_lm2, sig_4=sig_4_lm2, m=m_lm2, c=c_lm2,weights=None, scale_covar=False)
  
  
  print 'a_lm2_unc =', a_lm2.stderr
  </code></pre>
  
  <p>When I generate a fit report, I get uncertainty values so they are clearly being computed. My problem is calling them and using them. I tried to just print the uncertainty of the parameter using the stderr as in the last line of code above but this just returns 'None'. I can get a covariance matrix but I don't know what order this is being displayed in. My ultimate goal is simply to have the values and associated uncertainties that I can then put into an array and use further in my code.</p>