在MODX中使用一个代码片段自定义PHP

好的，所以我用PHP制作了一个计算器，并试图通过一个片段将其移植到MODX中。我试着把所有这些代码都放进代码片段中，但它不起作用。它一直给我一条错误消息，我无法查看该片段所在的资源。有人有什么想法吗？谢谢

<?php
function selected( $val = "")
{
$units = isset( $_POST['units'] ) ? $_POST['units'] : null;
echo ( $units == $val ) ? "CHECKED='CHECKED'" : "";
}
$units = isset( $_POST['units'] ) ? $_POST['units'] : null;
$dia = isset( $_POST['dia'] ) ? $_POST['dia'] : null;
$depth = isset( $_POST['depth'] ) ? $_POST['depth'] : null;
$L = isset( $_POST['L'] ) ? $_POST['L'] : null;
$num = isset($_POST['num']) ? $_POST['num'] : null;
$waste = isset($_POST['waste']) ? $_POST['waste'] : null;
$knownvolume = isset($_POST['knownvolume']) ? $_POST['knownvolume'] : null;
$hw = isset($_POST['hw']) ? $_POST['hw'] : null;
//$denom = ( ( $units == "US" ) ? 12 : 100 );
$tubecoverage = ( ( $units == "US" ) ? 18.59 : 304.65);
$onegalcoverage = ( ( $units == "US" ) ? 231 : 3785.41);
$twogalcoverage = ( ( $units == "US" ) ? 462 : 7470.82);
$fivegalcoverage = ( ( $units == "US" ) ? 1155 : 18927.06);
$measurements = 'in or cm';
    if( $units == 'US' ){
    $measurements = 'in';
}
    if($units == 'Metric')
{
    $measurements = 'cm';
}
if($units == 'US')
    $length = 'feet';
    else if($units == 'Metric')
    $length = 'meters';
    else 
    $length = 'feet or meters';
$tubes = ($tubes);
    if($knownvolume == TRUE)
    $tubes = (($knownvolume / $tubecoverage) * ($waste + 1) * 1.05);
    else 
    $tubes = (((($dia / 2) * ($dia / 2) * pi()) / $tubecoverage) * ($waste + 1) * 1.05);
$onegal = ($tubes);
    if($knownvolume == TRUE)
    $onegal = (($knownvolume / $onegalcoverage) * ($waste + 1) * 1.05);
    else 
    $onegal = (((($dia / 2) * ($dia / 2) * pi()) / $onegalcoverage) * ($waste + 1) *     1.05);
$twogal = ($tubes);
    if($knownvolume == TRUE)
    $twogal = (($knownvolume / $twogalcoverage) * ($waste + 1) * 1.05);
    else 
    $twogal = (((($dia / 2) * ($dia / 2) * pi()) / $twogalcoverage) * ($waste + 1) * 1.05);
$fivegal = ($tubes);
    if($knownvolume == TRUE)
    $fivegal = (($knownvolume / $fivegalcoverage) * ($waste + 1) * 1.05);
    else 
$fivegal = (((($dia / 2) * ($dia / 2) * pi()) / $fivegalcoverage) * ($waste + 1) * 1.05);
?>
<form method='post' action=''>
<table border='0' width='500px' cellpadding='2' cellspacing='1' class="calculator">
<tr class="calcheading"><td><label><input type="radio" name="units" 
<?php  selected("US")?> value="US" />S.A.E.</label>
<label><input type="radio" name="units" <?php selected("Metric")?> value="Metric"   />Metric</label> </td></tr>
<tr class="calcheading"><td colspan="2"><strong>Cicular Volume Area</strong></td></tr>
<tr class="calcrow"><td>Known Volume (<?php echo $measurements ?>):</td><td align="center"><input type='text' name='knownvolume' value="<?php echo $knownvolume ?>"/>     </td></tr>
<tr class="calcrow2"><td>Dia (<?php echo $measurements ?>):</td><td align="center"><input type='text' name='dia' value="<?php echo $dia ?>"/></td></tr>
<tr class="calcrow"><td>Length (<?php echo $measurements ?>):</td><td align="center"><input type='text' name='L' value="<?php echo $L ?>"/></td></tr>
<tr class="calcrow"><td>Waste Variance % (Please add in decimal form):</td><td     align="center"><input type='text' name='waste' value="<?php echo $waste ?>"/></td></tr>
<tr class="submit"><td colspan="2"><input type='submit' value='Calculate'/></td></tr>
<tr class="calcrow">
<td><i>10.3 oz Tube(s) (CS-1500):</td>
<td align="center"><input type="text" value="<?php echo round($tubes, 2)?>"/></td></i>
</tr>
<tr class="calcrow">
<td><i>1 Gallon Bucket(s) (CS-1000):</td>
<td align="center"><input type="text" value="<?php echo round($onegal, 2)?>"/></td></i>
</tr>
<tr class="calcrow">
<td><i>2 Gallon Bucket(s) (CS-1800):</td>
<td align="center"><input type="text" value="<?php echo round($twogal, 2)?>"/></td></i>
</tr>
<tr class="calcrow">
<td><i>5 Gallon Bucket(s) (CS-1000/CS-1500):</td>
<td align="center"><input type="text" value="<?php echo round($fivegal, 2)?>"/></td></i>
</tr>
</table>
</form>