From 0a48cad1c3a034ad1a48e811649148f4670d8f0c Mon Sep 17 00:00:00 2001
From: pazis <pazis.x@gmail.com>
Date: Mon, 23 Mar 2020 02:05:05 +0000
Subject: [PATCH] BAEL-3881

---
 algorithms-miscellaneous-6/pom.xml            | 15 +++++++++
 .../gradientdescent/GradientDescent.java      | 33 +++++++++++++++++++
 .../GradientDescentUnitTest.java              | 20 +++++++++++
 pom.xml                                       |  2 ++
 4 files changed, 70 insertions(+)
 create mode 100644 algorithms-miscellaneous-6/pom.xml
 create mode 100644 algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/gradientdescent/GradientDescent.java
 create mode 100644 algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/gradientdescent/GradientDescentUnitTest.java

diff --git a/algorithms-miscellaneous-6/pom.xml b/algorithms-miscellaneous-6/pom.xml
new file mode 100644
index 0000000000..5daa000ea3
--- /dev/null
+++ b/algorithms-miscellaneous-6/pom.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>algorithms-miscellaneous-6</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>algorithms-miscellaneous-6</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+</project>
diff --git a/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/gradientdescent/GradientDescent.java b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/gradientdescent/GradientDescent.java
new file mode 100644
index 0000000000..c5db3a4a06
--- /dev/null
+++ b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/gradientdescent/GradientDescent.java
@@ -0,0 +1,33 @@
+package com.baeldung.algorithms.gradientdescent;
+
+import java.util.function.Function;
+
+public class GradientDescent {
+
+    private final double precision = 0.000001;
+
+    public double findLocalMinimum(Function<Double, Double> f, double initialX) {
+        double stepCoefficient = 0.1;
+        double previousStep = 1.0;
+        double currentX = initialX;
+        double previousX = initialX;
+        double previousY = f.apply(previousX);
+        int iter = 100;
+
+        currentX += stepCoefficient * previousY;
+
+        while (previousStep > precision && iter > 0) {
+            iter--;
+            double currentY = f.apply(currentX);
+            if (currentY > previousY) {
+                stepCoefficient = -stepCoefficient / 2;
+            }
+            previousX = currentX;
+            currentX += stepCoefficient * previousY;
+            previousY = currentY;
+            previousStep = StrictMath.abs(currentX - previousX);
+        }
+        return currentX;
+    }
+
+}
diff --git a/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/gradientdescent/GradientDescentUnitTest.java b/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/gradientdescent/GradientDescentUnitTest.java
new file mode 100644
index 0000000000..34d3e188f2
--- /dev/null
+++ b/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/gradientdescent/GradientDescentUnitTest.java
@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.gradientdescent;
+
+import static org.junit.Assert.assertTrue;
+
+import java.util.function.Function;
+
+import org.junit.Test;
+
+public class GradientDescentUnitTest {
+
+    @Test
+    public void givenFunction_whenStartingPointIsOne_thenLocalMinimumIsFound() {
+        Function<Double, Double> df = x ->
+            StrictMath.abs(StrictMath.pow(x, 3)) - (3 * StrictMath.pow(x, 2)) + x;
+        GradientDescent gd = new GradientDescent();
+        double res = gd.findLocalMinimum(df, 1);
+        assertTrue(res > 1.78);
+        assertTrue(res < 1.84);
+    }
+}
diff --git a/pom.xml b/pom.xml
index 15331d8c95..45bdf9747e 100644
--- a/pom.xml
+++ b/pom.xml
@@ -342,6 +342,7 @@
                 <module>algorithms-miscellaneous-3</module>
                 <module>algorithms-miscellaneous-4</module>
                 <module>algorithms-miscellaneous-5</module>
+                <module>algorithms-miscellaneous-6</module>
                 <module>algorithms-searching</module>
                 <module>algorithms-sorting</module>
                 <module>algorithms-sorting-2</module>
@@ -853,6 +854,7 @@
                 <module>algorithms-miscellaneous-3</module>
                 <module>algorithms-miscellaneous-4</module>
                 <module>algorithms-miscellaneous-5</module>
+                <module>algorithms-miscellaneous-6</module>
                 <module>algorithms-searching</module>
                 <module>algorithms-sorting</module>
                 <module>algorithms-sorting-2</module>