add scalar product function

src/Phpml/Math/Product.php

@@ -0,0 +1,25 @@
+<?php
+declare(strict_types = 1);
+
+namespace Phpml\Math;
+
+class Product
+{
+
+    /**
+     * @param array $a
+     * @param array $b
+     *
+     * @return mixed
+     */
+    public function scalar(array $a, array $b)
+    {
+        $product = 0;
+        foreach ($a as $index => $value) {
+            $product += $value * $b[$index];
+        }
+
+        return $product;
+    }
+
+}

tests/Phpml/Math/ProductTest.php

@@ -0,0 +1,20 @@
+<?php
+declare(strict_types = 1);
+
+namespace tests\Phpml\Math;
+
+use Phpml\Math\Product;
+
+class ProductTest extends \PHPUnit_Framework_TestCase
+{
+
+    public function testScalarProduct()
+    {
+        $product = new Product();
+
+        $this->assertEquals(10, $product->scalar([2, 3], [-1, 4]));
+        $this->assertEquals(-0.1, $product->scalar([1, 4, 1], [-2, 0.5, -0.1]));
+        $this->assertEquals(8, $product->scalar([2], [4]));
+    }
+
+}