12.4. Fit Results and Outputs¶
Changed in version 0.9.34: minimize()
returns a result group containing fit statistics.
After the fit has completed, several statistics are output and available to
describe the quality of the fit and the estimated values for the Parameter
values and uncertainties. The main statistics are written to group
returned by minimize()
, while the parameter values in paramgroup
are updated to their bestfit values.
The estimated values, uncertainties, and correlations for each varied
Parameter are written as attributes of that Parameter. Thus, after a fit,
each variable Parameter par
will be updated so that par.value
will
hold the estimated bestfit value, par.stderr
will hold the estimated
uncertainty (1\(\sigma\) standard error), and par.correl
will hold
a dictionary of correlation values with the other variable Parameters.
General Fit statistics describing the quality of the fit and details about how the fit proceeded will be put into the result group with variable names and meanings as outlines in Table of Fit Statistics. For advanced users, the fitting class instance and result from lmfit are available.
Table of Fit Statistics and Results contained in the return value of
minimize()
.Listed are the names and description of items in the fit result group returned by the
minimize()
function. Many of these items are directly from lmfit.
name
Description of Statistical Quantity or Output
nvarys
number of variable parameters in the fit
ndata
number of data points
nfree
ndata  nfree
chi_square
chisquare: \(\chi^2 = \sum_i^N [{\rm Resid}_i]^2\)
chi_reduced
reduced chisquare: \(\chi^2_{\nu}= {\chi^2} / {(N  N_{\rm varys})}\) 
aic
bic
residual
final residual array
covar
covariance matrix (ordered according to var_names).
var_names
list of variable parameter names
params
lmfit Parameters
fitter
lmfit Minimizer
fit_details
lmfit MinimizerResult
nfev
number of evaluations of the fit residual function.
success
bool (True or False) for whether fit appeared to succeed.
errorbars
bool (True or False) for whether uncertainties were estimated.
message
text message from fit
lmdif_message
text message from Fortran leastsquares function
Changed in version 0.9.34: fit_report()
uses a result group returned by minimize()

fit_report
(result, show_correl=True, min_correl=0.1)¶ returns a fit report for a fit given a parameter group.
 Parameters
result – fit result group, returned by
minimize()
.show_correl – flag (
True
/False
) to show parameter correlations.min_correl – smallest absolute value of correlation to show.
 Returns
string of fit report. This can be printed or stored.
A typical result from fit_report()
would look like this:
larch> print fit_report(result)
[[Fit Statistics]]
# function evals = 28
# data points = 201
# variables = 4
chisquare = 0.50471
reduced chisquare = 0.002562
Akaike info crit = 1195.4
Bayesian info crit = 1182.2
[[Variables]]
amp: 12.0312835 +/ 0.076725 (0.64%) (init= 5)
wid: 2.01663402 +/ 0.011920 (0.59%) (init= 1)
off: 0.99188155 +/ 0.005226 (0.53%) (init= 0)
cen: 1.49995279 +/ 0.010144 (0.68%) (init= 2)
[[Correlations]] (unreported correlations are < 0.100)
C(amp, off) = 0.730
C(amp, wid) = 0.719
C(wid, off) = 0.525