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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# ELOGD -- Extended range log function.  Logarithmic scaling function for
+# negative or partially negative data.  The function is piecewise, continuous,
+# monotonic, reasonably smooth, and most importantly, is defined for all x.
+#
+#			     10.0 < X		y = log(x)
+#	       -10.0 <= X <= 10.0		y = x / 10.0
+#	   X < -10.0				y = -log(-x)
+#
+# Axes scaled with this function should have ticks labelled, e.g., 10**3,
+# 10**2, 10**1, 0, -10**1, -10**2, -10**3.  The corresponding ticks for
+# the normal log function would have values like 10**-2 rather than -10**2,
+# hence it is not difficult to distinguish between the two functions.
+
+double procedure elogd (x)
+
+double	x
+
+begin
+	if (x > 10.0D0)
+	    return (log10 (x))
+	else if (x >= -10.0D0)
+	    return (x / 10.0D0)
+	else
+	    return (-log10 (-x))
+end