add cosine similarity function to vector class (#35)

Co-authored-by: 권욱진 <[email protected]>
Co-authored-by: battlecook <[email protected]>

src/Vector.php

@@ -82,6 +82,21 @@ public function magnitude()
         return $this->length();
     }
 
+    /**
+     * @param self $other
+     * @return float
+     * @throws VectorException
+     * @link https://en.wikipedia.org/wiki/Cosine_similarity
+     */
+    public function cosineSimilarity(self $other): float
+    {
+        if ($other->getSize() !== $this->getSize()) {
+            throw new VectorException('Vectors have to have same size');
+        }
+
+        return $this->dotProduct($other) / ($this->l2Norm() * $other->l2Norm());
+    }
+
     /**
      * @param self $other
      * @return float

tests/VectorTest.php

@@ -106,6 +106,14 @@ public function testDotProduct()
         $this->assertEquals((1 * -1) + (2 * 3) + (3 * 5) + (4 * 2), $vector1->dotProduct($vector2));
     }
 
+    public function testCosineSimilarity()
+    {
+        $vector1 = new Vector([1, 0, 1, 1]);
+        $vector2 = new Vector([2, 0, 2, 2]);
+
+        $this->assertEquals(1.00, $vector1->cosineSimilarity($vector2));
+    }
+
     public function testOuterProduct()
     {
         $vector1 = new Vector([1, 2]);