PHP resize image by width or heigth or both

resize.php

<?php

/**
 * Basic function for resize. It doesn't save image. To save use imagejpeg()
 */
function resize($width = null, $height = null)
{
    if (!$width && !$height) {
        return false;
    }

    $original = 'image.jpg';

    list($originalWidth, $originalHeight) = getimagesize($original);

    if (!$height) {
        $height = round((($originalHeight * $width) / $originalWidth));
    } elseif (!$width) {
        $width = round((($originalWidth * $height) / $originalHeight));
    }

    $destinationImage= imagecreatetruecolor($width, $height);
    $sourceImage = imagecreatefromjpeg($original);
    imagecopyresampled($destinationImage, $sourceImage, 0, 0, 0, 0, $width, $height, $originalWidth, $originalHeight));
}