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diff --git a/math/nlfit/nlfitdef.gh b/math/nlfit/nlfitdef.gh
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+# The NLFIT data structure.
+
+# Structure length
+define	LEN_NLSTRUCT	35
+
+
+# Structure definition
+define  NL_TOL          Mem$t[P2$T($1+0)]   # Tolerance for convergence
+define  NL_LAMBDA       Mem$t[P2$T($1+2)]   # Damping factor
+define	NL_OLDSQ	Mem$t[P2$T($1+4)]   # Sum resid. squared last iter.
+define	NL_SUMSQ	Mem$t[P2$T($1+6)]   # Sum of residuals squared 
+define	NL_REFSQ	Mem$t[P2$T($1+8)]   # Reference sum of squares
+define	NL_SCATTER	Mem$t[P2$T($1+10)]  # Additional scatter
+
+define	NL_FUNC		Memi[$1+12]	# Fitting function
+define	NL_DFUNC	Memi[$1+13]	# Derivative function
+define	NL_NPARAMS	Memi[$1+14]	# Number of parameters
+define	NL_NFPARAMS	Memi[$1+15]	# Number of fitted parameters
+define	NL_ITMAX	Memi[$1+16]	# Max number of iterations
+define	NL_ITER		Memi[$1+17]	# Iteration counter
+define	NL_NPTS		Memi[$1+18]	# Number of points in fit
+
+define	NL_PARAM	Memi[$1+19]	# Pointer to parameter vector
+define	NL_OPARAM	Memi[$1+20]	# Pointer to orignal parameter vector
+define	NL_DPARAM	Memi[$1+21]	# Pointer to parameter change vector
+define	NL_DELPARAM	Memi[$1+22]	# Pointer to delta param vector
+define	NL_PLIST	Memi[$1+23]	# Pointer to parameter list
+define	NL_ALPHA	Memi[$1+24]	# Pointer to alpha matrix
+define	NL_COVAR	Memi[$1+25]	# Pointer to covariance matrix
+define	NL_BETA		Memi[$1+26]	# Pointer to beta matrix
+define	NL_TRY		Memi[$1+27]	# Pointer to trial vector
+define	NL_DERIV	Memi[$1+28]	# Pointer to derivatives
+define	NL_CHOFAC	Memi[$1+29]	# Pointer to Cholesky factorization
+
+# next free location	($1 + 30)
+
+# Access to buffers
+define	PLIST		Memi[$1]	# Parameter list
+define	OPARAM		Mem$t[P2P($1)]	# Original parameter vector
+define	PARAM		Mem$t[P2P($1)]	# Parameter vector
+define	DPARAM		Mem$t[P2P($1)]	# Parameter change vector
+define	ALPHA		Mem$t[P2P($1)]	# Alpha matrix
+define	BETA		Mem$t[P2P($1)]	# Beta matrix
+define	TRY		Mem$t[P2P($1)]	# Trial vector
+define	DERIV		Mem$t[P2P($1)]	# Derivatives
+define	CHOFAC		Mem$t[P2P($1)]	# Cholesky factorization
+define	COVAR		Mem$t[P2P($1)]	# Covariance matrix
+
+# Defined constants alter for tricky problems
+define	LAMBDAMAX	1000.0
+define	MINITER		3