feat: add vector\add()

composer.json

@@ -20,7 +20,8 @@
     },
     "autoload": {
         "files": [
-            "src/array.php"
+            "src/array.php",
+            "src/vector.php"
         ],
         "psr-4": {
             "empaphy\\maphematics\\": "src/"

src/vector.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace empaphy\maphematics\vector;
+
+use empaphy\maphematics\array;
+
+/**
+ * Add two or more vectors together.
+ *
+ *     ⎡ a ⎤   ⎡ x ⎤   ⎡ a + x ⎤
+ *     ⎢ b ⎥ + ⎢ y ⎥ = ⎢ b + y ⎥
+ *     ⎣ c ⎦   ⎣ z ⎦   ⎣ c + z ⎦
+ *
+ * @param  array<int|float>  $vector
+ * @param  array<int|float>  ...$vectors
+ * @return array<int|float>
+ */
+function add(array $vector, array ...$vectors): array
+{
+    $vectors = [$vector, ...$vectors];
+    $length  = array\check_lengths(...$vectors);
+    $count   = \count($vectors);
+    $result  = \array_fill(0, $length, 0);
+
+    for ($i = 0; $i < $length; $i++) {
+        for ($j = 0; $j < $count; $j++) {
+            $result[$i] += $vectors[$j][$i];
+        }
+    }
+
+    return $result;
+}

tests/Unit/VectorTest.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * Vector tests.
+ *
+ * @noinspection StaticClosureCanBeUsedInspection
+ */
+
+use empaphy\maphematics\vector;
+
+describe('vector\add', function () {
+    it('works', function ($vector, $vectors, $expected) {
+        expect(vector\add($vector, ...$vectors))->toBe($expected);
+    })->with([
+        'two vectors'         => [[3, -5], [[2, 1]], [3 + 2, -5 + 1]],
+        'three vectors'       => [[1, 2], [[3, 5], [7, 11]], [1 + 3 + 7, 2 + 5 + 11]],
+        'vectors with floats' => [[3.0, -5.0], [[2.0, 1.0]], [3.0 + 2.0, -5.0 + 1.0]],
+    ]);
+});