From 03e2fc959702e7654c507c4c6125ea1c1b54ecb6 Mon Sep 17 00:00:00 2001
From: Benjamin Culkin <bjculkin@mix.wvu.edu>
Date: Mon, 5 Feb 2018 13:01:44 -0800
Subject: Add dual numbers

Dual numbers are a easy way of doing automatic numeric differentiation
of expressions.
---
 base/src/main/java/bjc/utils/math/Dual.java | 83 +++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 base/src/main/java/bjc/utils/math/Dual.java

(limited to 'base/src/main/java/bjc/utils/math/Dual.java')

diff --git a/base/src/main/java/bjc/utils/math/Dual.java b/base/src/main/java/bjc/utils/math/Dual.java
new file mode 100644
index 0000000..53ddc32
--- /dev/null
+++ b/base/src/main/java/bjc/utils/math/Dual.java
@@ -0,0 +1,83 @@
+package bjc.utils.math;
+
+/**
+ * Represents a 'dual' number.
+ *
+ * Think imaginary numbers, where instead of i, we add a value d such that d^2 =
+ * 0.
+ */
+public class Dual {
+	/**
+	 * The real part of the dual number.
+	 */
+	public double real;
+	/**
+	 * The dual part of the dual number.
+	 */
+	public double dual;
+
+	/**
+	 * Create a new dual with both parts zero.
+	 */
+	public Dual() {
+		real = 0;
+		dual = 0;
+	}
+
+	/**
+	 * Create a new dual number with a zero dual part.
+	 *
+	 * @param real
+	 *                The real part of the number.
+	 */
+	public Dual(double real) {
+		this.real = real;
+		this.dual = 0;
+	}
+
+	/**
+	 * Create a new dual number with a specified dual part.
+	 *
+	 * @param real
+	 *                The real part of the number.
+	 * @param dual
+	 *                The dual part of the number.
+	 */
+	public Dual(double real, double dual) {
+		this.real = real;
+		this.dual = dual;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("<%f, %f>", real, dual);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		long temp;
+		temp = Double.doubleToLongBits(dual);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		temp = Double.doubleToLongBits(real);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		Dual other = (Dual) obj;
+		if (Double.doubleToLongBits(dual) != Double.doubleToLongBits(other.dual))
+			return false;
+		if (Double.doubleToLongBits(real) != Double.doubleToLongBits(other.real))
+			return false;
+		return true;
+	}
+}
\ No newline at end of file
-- 
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