.help nlfit Feb91 "Nlfit Package"
.ih
NAME
nlfit -- fit a curve to a set of data values
.ih
SYNOPSIS
nlfit (nl, x, z, w, npts, nvars, wtflag, ier)

.nf
pointer		nl		# curve descriptor
real/double	x[npts*nvars]	# variable values (stored as x[nvars,npts])
real/double	z[npts]		# array of z values
real/double	w[npts]		# array of weights
int		npts		# number of data points
int		wtflag		# type of weighting
int		ier		# error code
.fi
.ih
ARGUMENTS
.ls nl    
Pointer to the curve descriptor structure.
.le
.ls x    
Array of x values.
.le
.ls z
Array of function values.
.le
.ls w
Array of weights.
.le
.ls npts
The number of data points.
.le
.ls wtflag
Type of weighting. The options are WTS_USER, WTS_UNIFORM, WTS_CHISQ and
WTS_SCATTER. If wtflag = WTS_USER individual weights for each data point
are supplied by the calling program and points with zero-valued weights are
not included in the fit. If wtflag = WTS_UNIFORM, all weights are assigned
values of 1. If wtflag = WTS_CHISQ the weights are set equal to the
reciprocal of the function value. If wtflag = WTS_SCATTER the fitting
routine adds a scatter term to the weights if the reduced chi-squared of
the fit is significantly greater than 1.
.le
.ls ier
Error code for the fit. The options are DONE, SINGULAR,
NO_DEG_FREEDOM and NOT_DONE. If ier = SINGULAR, the numerical routines
will compute a
solution but one or more of the coefficients will be
zero. If ier = NO_DEG_FREEDOM, there were too few data points to solve the
matrix equations and the routine returns without fitting the data.
If ier = NOT_DONE, the fit could not achieve the desired tolerance with
the given input data in the specified maximum number of iterations.
.le
.ih
DESCRIPTION
NLFIT accumulate the data into the appropriate internal matrices and vectors
and does the fit.
.ih
NOTES
The permitted values of the input wtflag argument to nlfit[rd] are the
following.

.nf
define	WTS_USER			# User enters weights
define	WTS_UNIFORM			# Equal weights
define	WTS_CHISQ 			# Chi-squared weights
define	WTS_SCATTER			# Weights include scatter term
.fi

The permitted error values returned from nlfit[rd] are the following.

.nf
define	DONE			0	# Solution converged
define	SINGULAR		1	# Singular matrix
define	NO_DEG_FREEDOM		2	# Too few points
define	NOT_DONE		3	# Solution did not converge
.fi
.ih
SEE ALSO
.endhelp