.help nlinit Feb91 "Nlfit Package"
.ih
NAME
nlinit -- initialise curve descriptor
.ih
SYNOPSIS
include <math/nlfit.h>

nlinit[rd] (nl, fnc, dfnc, params, dparams, nparams, plist, nfparams,
                tol, itmax)

.nf
pointer		nl		# curve descriptor
int		fnc		# address of first user-supplied function
int		dfnc		# address of second user-supplied function
real/double	params[nparams]	# list of initial parameter values
real/double	dparams[nparams]# list of parameter increments
int		nparams		# number of parameters
int		plist[nparams]	# list of parameters to be fit
int		nfparams	# number of parameters to be fit
real/double	tol		# fitting tolerance
int		itmax		# maximum number of iterations
.fi
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ARGUMENTS
.ls nl             
Pointer to the curve descriptor structure.
.le
.ls fnc       
The address of the user-supplied subroutine fncname for evaluating the function
to be fit. The calling sequence of fncname is the following.

.nf
fncname (x, nvars, params, nparams, zfit)
.fi
.le
.ls dfnc       
The address of the user-supplied subroutine dfncname for evaluating the
function to be fit and its derivatives with respect to the parameters.
The calling sequence of dfncname is the following.

.nf
dfncname (x, nvars, params, dparams, nparams, zfit, derivs)
.fi
.le
.ls params
An array containing initial values of all the parameters, including both
those to be fit and those that are to be held constant.
.le
.ls dparams
An array parameter increment values over which the derivatives are to be
computed empirically. If equations are supplied for the derivatives
inside dfnc, the dparams array is not used.
.le
.ls nparams
The total number of parameters in the user-supplied function.
.le
.ls plist
The list of parameters to be fit. Plist is an integer array containing
the indices of those parameters in params to be fit.
.le
.ls nfparams
The total number of parameters to be fit.
.le
.ls tol   
The fitting tolerance. If the difference in the chi-squared
from one iteration to the next is less than the fitting tolerance
times the current chi-squared, the fit has converged.
.le
.ls itmax
The maximum number of fitting iterations. Itmax must be greater than
or equal to 3.
.le
.ih
DESCRIPTION
Allocate space for the curve descriptor structure and the arrays and
vectors used by the numerical routines. Initialize all arrays and vectors
to zero. Return the curve descriptor to the calling routine.
.ih
NOTES
NLINIT must be the first NLFIT routine called. NLINIT returns a NULL pointer
if it encounters an illegal parameter list.
.ih
SEE ALSO
nlfree
.endhelp
