Clean up Java implementation of Thomas Algorithm (#496)

Author: Butt4cak3

contents/thomas_algorithm/code/java/Thomas.java

@@ -0,0 +1,43 @@
+public class Thomas {
+    private static double[] thomasAlgorithm(double[] a, double[] b, double[] c, double[] x) {
+        int size = a.length;
+        double[] y = new double[size]; // This is needed so that we don't have to modify c
+        double[] solution = new double[size];
+
+        // Set initial elements
+        y[0] = c[0] / b[0];
+        solution[0] = x[0] / b[0];
+
+        for (int i = 1; i < size; ++i) {
+            // Scale factor is for c and x
+            double scale = 1.0 / (b[i] - a[i] * y[i - 1]);
+            y[i] = c[i] * scale;
+            solution[i] = (x[i] - a[i] * solution[i - 1]) * scale;
+        }
+
+        // Back-substitution
+        for (int i = size - 2; i >= 0; --i) {
+            solution[i] -= y[i] * solution[i + 1];
+        }
+
+        return solution;
+    }
+
+    public static void main(String[] args) {
+        double[] a = {0.0, 2.0, 3.0};
+        double[] b = {1.0, 3.0, 6.0};
+        double[] c = {4.0, 5.0, 0.0};
+        double[] x = {7.0, 5.0, 3.0};
+        double[] solution = thomasAlgorithm(a, b, c, x);
+
+        System.out.format("The system,\n");
+        System.out.format("[%.1f, %.1f, %.1f][x] = [%.1f]\n", b[0], c[0], 0f, x[0]);
+        System.out.format("[%.1f, %.1f, %.1f][y] = [%.1f]\n", a[1], b[1], c[1], x[1]);
+        System.out.format("[%.1f, %.1f, %.1f][z] = [%.1f]\n", 0f, a[2], b[2], x[2]);
+        System.out.format("has the solution:\n");
+
+        for (int i = 0; i < solution.length; i++) {
+            System.out.format("[% .5f]\n", solution[i]);
+        }
+    }
+}

contents/thomas_algorithm/code/java/thomas.java

@@ -108,7 +108,7 @@ You will find this algorithm implemented [in this project](https://scratch.mit.e
   <img  class="center" src="code/scratch/thomas.svg" width="1000" />
 </p>
 {% sample lang="java" %}
-[import, lang:"java"](code/java/thomas.java)
+[import, lang:"java"](code/java/Thomas.java)
 {% sample lang="hs" %}
 [import, lang:"haskell"](code/haskell/thomas.hs)
 {% sample lang="go" %}