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+.help extrema Dec83 xtools
+.ih
+NAME
+extrema -- find the extrema in an array of x and y points
+.ih
+SYNOPSIS
+.nf
+nextrema = extrema (x, y, curvature, npts, dx)
+
+real	x[npts], y[npts]	# Input data points and output extrema
+real	curvature[npts]		# 2nd deriv. of cubic spline at extrema
+int	npts			# Number of input data points
+real	dx			# Precision of extrema positions
+.fi
+.ih
+DESCRIPTION
+The input data points are fitted with a cubic interpolation spline.  The
+spline is then searched for points where the first derivative changes sign.
+The minimum step size of this search is controlled by the parameter dx.
+The positions of these extrema are returned in the x array, the value of the
+spline at the extrema are returned in the y array, and the curvature or
+second derivative of the spline at the extrema are returned in the
+curvature array.  The function returns the number of extrema found.
+.ih
+SEE ALSO
+xtools.peaks
+.endhelp