Commands for creating, configuring, and running curve fits. See Curves & Fitting for a conceptual guide with worked examples, convolution, and parameter strategies.

Core commands

Command	Action
cc <expr>	Create curve attached to the current data file
cca <expr>	Create artificial curve (no data reference)
cm	Modify the curve expression interactively
cd <k>	Set the data file to fit (expression for k allowed)
cv <k>	Set convolution file; cv- disables convolution
cr	Set fit range restriction (expression selecting points)
cf	Run fit
cfs	Run fit, allow slow O(N²) convolution
cp	Print parameters
ci <n>	Extract parameter n into a new workspace; ci * for all
cx <n>	Fix parameter n (exclude from fit)
cu <n>	Unfix (release) parameter n
cg <n>	Make parameter n global

cg — global parameters

By default each spectrum in a curve file has its own independent copy of each parameter. Making a parameter global forces all spectra to share one common value for that parameter, which is then optimised jointly across all spectra during cf. Useful for a background or resolution shift that is known to be the same for every spectrum.

Weighting

The weighting scheme determines how residuals are weighted in the least-squares sum. The default cwv is appropriate when y values have associated error bars dy.

Command	Weighting scheme
cwc	Constant (all points equal weight)
cwl	Logarithmic
cwv	Reciprocal variance 1/dy² (default)
cwvd	Reciprocal variance, using data dy only
cwvc	Reciprocal variance, using curve dy only

Curve plotting options

Command	Action
cgd+	Evaluate curve at the x points of the data file
cgd-	Evaluate curve on an equidistant grid (default)

Fit solver settings

These settings rarely need changing. The defaults work for most fits.

Command	Action
csf	Gradient step factor
cse	Step size for numerical differentiation (√ε)
csc	Maximum number of solver calls
csv	Solver verbosity (0 = silent, higher = more output)
csm	Fit metric (least squares, etc.)
cst	Maximum fit duration (seconds)

Numerical integration settings

Used only when the curve expression contains an integral (e.g. a distribution model). Leave at defaults unless the solver reports integration errors.

Command	Action
cn?	Show current integration parameters
cnm	Integration mode
cna	Absolute error tolerance (eps_abs)
cnr	Relative error tolerance (eps_rel)