From b8d56dd7282bdca47c3d7c6d194efc26d00f838a Mon Sep 17 00:00:00 2001
From: zhaoliu <zhaoliu@freewheel.tv>
Date: Sun, 23 Sep 2018 17:06:06 +0800
Subject: [PATCH] Newton Raphson method.

---
 other/NewtonMethod.go | 58 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 other/NewtonMethod.go

diff --git a/other/NewtonMethod.go b/other/NewtonMethod.go
new file mode 100644
index 00000000..dcd40d19
--- /dev/null
+++ b/other/NewtonMethod.go
@@ -0,0 +1,58 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+const PRECISION = 0.000000001
+const maxRunLoop = 100
+
+func DichotomyEquation(a float64, b float64, f func(input float64) float64) (float64, int) {
+	mid := (a + b) / 2.0
+	count := 0
+	for ; (b - a) > PRECISION; {
+		if f(a)*f(mid) < 0.0 {
+			b = mid
+		} else {
+			a = mid
+		}
+		mid = (a + b) / 2.0
+		count++
+	}
+
+	return mid, count
+}
+
+func target(x float64) float64 {
+	return (2.0*x*x + 3.2*x - 1.8)
+}
+
+func CalcDerivative(f func(input float64) float64, x float64) float64 {
+	return (f(x+0.000005) - f(x-0.000005)) / 0.00001
+}
+
+func NewtonRaphson(f func(input float64) float64, x0 float64) (float64, int) {
+	var x float64 = math.MaxInt64
+	var count int = 0
+	for count < maxRunLoop {
+		x1 := x0 - f(x0)/CalcDerivative(f, x0)
+		if (math.Abs(x1-x0) < PRECISION) {
+			x = x1
+			break
+		}
+		x0 = x1
+		count++
+	}
+	return x, count
+}
+
+func main() {
+
+	fmt.Println("Use DichotomyEquation method")
+	mid, times := DichotomyEquation(-8.0, 8.0, target)
+	fmt.Printf("values is %f, run %d times", mid, times)
+	fmt.Println("Use Newton Raphson method")
+	mid1, times1 := NewtonRaphson(target, -8.0)
+	fmt.Printf("values is %f, run %d times", mid1, times1)
+}