/**
* Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
*
* Please see distribution for license.
*/
package com.opengamma.analytics.math.function.special;
import org.apache.commons.lang.Validate;
import com.opengamma.analytics.math.function.Function1D;
/**
* Class representing the top-hat function, defined as:
* $$
* \begin{align*}
* T(x)=
* \begin{cases}
* 0 & x < x_1\\
* y & x_1 < x < x_2\\
* 0 & x > x_2
* \end{cases}
* \end{align*}
* $$
* where $x_1$ is the lower edge of the "hat", $x_2$ is the upper edge and $y$
* is the height of the function.
*
* This function is discontinuous at $x_1$ and $x_2$.
*/
public class TopHatFunction extends Function1D<Double, Double> {
private final double _x1;
private final double _x2;
private final double _y;
/**
* @param x1 The lower edge
* @param x2 The upper edge, must be greater than x1
* @param y The height
*/
public TopHatFunction(final double x1, final double x2, final double y) {
Validate.isTrue(x1 < x2, "x1 must be less than x2");
_x1 = x1;
_x2 = x2;
_y = y;
}
/**
* @param x The argument of the function, not null. Must have $x_1 < x < x_2$
* @return The value of the function
*/
@Override
public Double evaluate(final Double x) {
Validate.notNull(x, "x");
Validate.isTrue(x != _x1, "Function is undefined for x = x1");
Validate.isTrue(x != _x2, "Function is undefined for x = x2");
if (x > _x1 && x < _x2) {
return _y;
}
return 0.;
}
}