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.help nlfit Feb91 "Nlfit Package"
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NAME
nlfit -- fit a curve to a set of data values
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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
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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
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DESCRIPTION
NLFIT accumulate the data into the appropriate internal matrices and vectors
and does the fit.
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NOTES
The permitted values of the input wtflag argument to nlfit[rd] are the
following.
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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
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