今月以外のカレンダーを表示する方法

<?php 
function calendar(){
    if($_SESSION["year"] == ""){
        $_SESSION["year"] = date(Y);
    }
    if($_SESSION["month"] == ""){
        $_SESSION["month"] = date(n);
    }
    /////////プルダウンリストから年を選んだ時の処理////////////
    if($_GET['year']){
        $_SESSION["year"] = $_GET['year'];
    }
     /////////プルダウンリストから月を選んだ時の処理////////////
    if($_GET['month']){
        $_SESSION["month"] = $_GET['month'];
    }
      /////////ココから今月の処理////////////
    if(@$_GET['kongetu']){
        $_SESSION["year"] = date(Y);
        $_SESSION["month"] = date(n);
    }
echo<<<EOT
<div class="calendar_box">
<div style="text-align:center;">
<div style="margin-left:auto; margin-right:auto;">
 
<form action="" method="GET">

<select name="year" onChange="submit()">
EOT;

    for ($i = 2016; $i <= 2020; $i++) {
        echo "<option value='".$i."'";
        if ($i == $_SESSION["year"]) echo " selected";
        $di = mb_convert_kana($i,A,"UTF8");
        echo ">".$di."年</option>\n";
    }
 
echo<<<EOT
</select>
<select name="month" onChange="submit()">
EOT;

    for ($i = 1; $i <= 12; $i++) {
        echo "<option value='".$i."'";
        if ($i == $_SESSION["month"]) echo " selected";
        $di = mb_convert_kana($i,A,"UTF8");
        echo ">".$di."月</option>\n";
    }
 
echo<<<EOT
</select>
<input type="submit" name="kongetu" value="今月">
</form>

</div>
</div>

EOT;

}
?><!--
<?php calendar(); ?>

<p><?php $this->BcBaser->scheduleCalendar($_SESSION["year"],$_SESSION["month"], array('title' => true)) ?></p>
<!--
<?php $this->BcBaser->getScheduleDatas($_SESSION["nen"], $_SESSION["tuki"]) ?>
<?php $this->BcBaser->schedules() ?>
-->