如何在php中计算两个向量代码之间的角度

function norm($vec)
{
    $norm = 0;
    $components = count($vec);

    for ($i = 0; $i < $components; $i++)
        $norm += $vec[$i] * $vec[$i];

    return sqrt($norm);
}

function dot($vec1,$vec2)
{
    $prod = 0;
    $components = count($vec1);

    for ($i = 0; $i < $components; $i++)
        $prod += ($vec1[$i] * $vec2[$i]);

    return $prod;
}

并计算实际角度：

$v1 = array(-1,-2);
$v2 = array(90,-5);

$ang = acos(dot($v1,$v2) / (norm($v1) * norm($v2)));

echo $ang; // angle in radians
> 1.97894543055