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diff --git a/ETL/tags/stable/ETL/_calculus.h b/ETL/tags/stable/ETL/_calculus.h
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+/*! ========================================================================
+** Extended Template and Library
+** Calculus Functional Classes Implementation
+** $Id$
+**
+** Copyright (c) 2002 Robert B. Quattlebaum Jr.
+**
+** This package is free software; you can redistribute it and/or
+** modify it under the terms of the GNU General Public License as
+** published by the Free Software Foundation; either version 2 of
+** the License, or (at your option) any later version.
+**
+** This package is distributed in the hope that it will be useful,
+** but WITHOUT ANY WARRANTY; without even the implied warranty of
+** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+** General Public License for more details.
+**
+** === N O T E S ===========================================================
+**
+** ========================================================================= */
+
+/* === S T A R T =========================================================== */
+
+#ifndef __ETL__CALCULUS_H
+#define __ETL__CALCULUS_H
+
+/* === H E A D E R S ======================================================= */
+
+#include <functional>
+
+/* === M A C R O S ========================================================= */
+
+//#ifndef _EPSILON
+//#define _EPSILON		0.0000001
+//#endif
+
+#define ETL_FIXED_DERIVATIVE 1
+
+/* === T Y P E D E F S ===================================================== */
+
+/* === C L A S S E S & S T R U C T S ======================================= */
+
+_ETL_BEGIN_NAMESPACE
+
+template <typename T>
+class derivative : public std::unary_function<typename T::argument_type,typename T::result_type>
+{
+	T func;
+	typename T::argument_type epsilon;
+public:
+	explicit derivative(const T &x, const typename T::argument_type &epsilon=0.000001):func(x),epsilon(epsilon) { }
+
+	typename T::result_type
+	operator()(const typename T::argument_type &x)const
+	{
+#ifdef ETL_FIXED_DERIVATIVE
+		return (func(x+epsilon)-func(x))/epsilon;
+#else
+		return (func(x)-func(x+epsilon))/epsilon;
+#endif
+	}
+};
+
+template <typename T>
+class integral : public std::binary_function<typename T::argument_type,typename T::argument_type,typename T::result_type>
+{
+	T func;
+	int samples;
+public:
+	explicit integral(const T &x, const int &samples=500):func(x),samples(samples) { }
+
+	typename T::result_type
+	operator()(typename T::argument_type x,typename T::argument_type y)const
+	{
+		typename T::result_type ret=0;
+		int i=samples;
+		const typename T::argument_type increment=(y-x)/i;
+
+		for(;i;i--,x+=increment)
+			ret+=(func(x)+func(x+increment))*increment/2;
+		return ret;
+	}
+};
+
+_ETL_END_NAMESPACE
+
+/* === E N D =============================================================== */
+
+#endif