Re: Calculation error - PHP not following math hierarchi ???

See http://us3.php.net/manual/en/language.operators.php http://us3.php.net/manual/en/language.operators.bitwise.php You want this: function calc_distance($curX,$curY,$newX,$newY) { // calculate distance to new location $distX = abs($curX - $newX); $distY = abs($curY - $newY); if ($distX <= 150 && $distY <= 150) { $dist = sqrt(pow( $distX,2) + pow($distY,2)); } elseif ($distX > 150 && $distY <= 150) { $dist = sqrt(pow((abs(300 - $newX)),2) + pow($distY,2)); } elseif ($distX <= 150 && $distY > 150) { $dist = sqrt(pow($distX,2) + pow((abs(300 - $newY)),2)); } else { $dist = sqrt(pow((abs(300 - $newX)),2) + pow((abs(300 - $newY)),2)); } return $dist; } echo calc_distance( 150, 150, 300, 300 ); //echoes 212.13203435596 echo "<br>150^2=".(150^2)." and pow(150,2)=".(pow(150,2)); //echoes 150^2=148 and pow(150,2)=22500 kgt Rene Brehmer wrote:

I've run into a situation where PHP is way off when doing a relatively simple calculation of distance between two points in 2-dimensional space, where coordinates go from 1 to 300 in both X and Y directions. When passing 300, it goes back to 1, and vise-versa (it's for a game and is supposed to approximate the movement over a sphere). Using this function: function calc_distance($curX,$curY,$newX,$newY) { // calculate distance to new location $distX = abs($curX - $newX); $distY = abs($curY - $newY); if ($distX <= 150 && $distY <= 150) { $dist = sqrt($distX^2 + $distY^2); } elseif ($distX > 150 && $distY <= 150) { $dist = sqrt((abs(300 - $newX))^2 + $distY^2); } elseif ($distX <= 150 && $distY > 150) { $dist = sqrt($distX^2 + (abs(300 - $newY))^2); } else { $dist = sqrt((abs(300 - $newX))^2 + (abs(300 - $newY))^2); } return $dist; } And using 150,150 as $curX,$curY and 300,300 as $newX,$newY ... PHP calculates $dist as 3.46410161514 which obviously is far off target ...referring to my calcultor, the correct result for the same code is supposed to be 212.1320 What happens here ? And how the heck do I get to calculate right ? Float errors usually isn't this severe, so I'm assuming it's a problem with properly acknowledging the hierarchi of the mathematical operators ... It's PHP ver. 4.3.0, on Apache/2.0.53 (Win32), on WinXP SP1 I've been trying to manually calculate the formula out of order to figure out how the strange result comes about, but haven't had any success yet ... Any suggestions ? Rene