Find the heat index temperature in PHP.

heat_index.php

<?php
/* 
 * The heat index formula in PHP
 * https://en.wikipedia.org/wiki/Heat_index#Formula
 */

function hi($T,$rh) {
  $c1 = -42.379;
  $c2 = 2.04901523;
  $c3 = 10.14333127;
  $c4 = -0.22475541;
  $c5 = -6.83783 * pow(10, -3);
  $c6 = -5.481717 * pow(10, -2);
  $c7 = 1.22874 * pow(10, -3);
  $c8 = 8.5282 * pow(10, -4);
  $c9 = -1.99 * pow(10, -6);

  $hi = $c1 + $c2*$T + $c3*$rh + $c4*$T*$rh + $c5*$T*$T + $c6*$rh*$rh + $c7*$T*$T*$rh + $c8*$T*$rh*$rh + $c9*$T*$T*$rh*$rh;

  return round($hi);
}
?>