笛卡尔的情书r=a(1-sinθ)

<?php
$width = 600;
$height = 650;
header("Content-type: image/gif");
$img = imagecreate($width, $height); 
$bg_color = imagecolorallocate($img, 0, 0, 0);
$red = imagecolorallocate($img, 255, 0, 0);
for ($i = 0; $i <= 100; $i++) {
    for ($j = 0; $j <= 100; $j++) {
        $r = M_PI / 50 * $i * (1 - sin(M_PI / 50 * $j)) * 40;
        $x = $r * cos(M_PI / 50 * $j) * sin(M_PI / 50 * $i) + $width / 2;
        $y = -$r * sin(M_PI / 50 * $j) + $height / 6;
        imagesetpixel($img, $x, $y, $red);
    }
}
imagegif($img);
imagedestroy($img);exit;<?php
$width = 600;
$height = 650;
header("Cont