Placing distance into variable from geocoordinates script

Hi Everyone,
I’m building out a loop that I want to be able to display the distance in miles for each post based on variables containing the coordinates of one point and the coordinates of another. I have point A and B’s individual latitude and longitude values inside of custom fields.

I found a script that is a good starting point, but no matter how I try to place Point A and B’s values, it crashes and the page either quits loading at that point, or I get the PHP white screen of death.

Here’s the script I’m starting from:

<?php
function distance($lat1, $lon1, $lat2, $lon2, $unit) {

  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
    } else {
        return $miles;
      }
}

echo distance(32.9697, -96.80322, 29.46786, -98.53506, "M") . " Miles<br>";

?>

And here’s an example of how I’ve tried getting the variables into the script:

<?php
function distance($lat1, $lon1, $lat2, $lon2, $unit) {

  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
    } else {
        return $miles;
      }
}

echo distance('.$a_lat.', '.$a_long.', '.$b_lat.', '.$b_long.', "M") . " Miles<br>";

?>

My question is: How can I properly echo out the variables into this script so that it shows up with each post in the loop?

Thanks!