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Bug #20346 Computation Error
Submitted: 2002-11-10 15:44 UTC Modified: 2002-11-10 16:54 UTC
From: sprice at wisc dot edu Assigned:
Status: Not a bug Package: Math related
PHP Version: 4CVS-2002-11-10 OS: Darwin 6.1 (Mac OS X.2.1)
Private report: No CVE-ID: None
 [2002-11-10 15:44 UTC] sprice at wisc dot edu
On this one, I really don't have a clue what is wrong with PHP. Run the script shown below. Results should be "c" == "d" == "e", but "e" is some other value. I noticed that if you comment out the "$temp_x = ..." line (which shouldn't matter anyway) you get the correct answer for "e". I need this to convert a vector to unit length (which should be simple enough) and I thought that I was going crazy.

If you want to see how PHP is configured, look here:
http://144.92.10.251/~sage/test.php

<?php
$temp_x = .0663;
$temp_y = .01486;

print "a=" . $temp_x . ", b=" . $temp_y . ", c=" .
	(.0148 / sqrt( .0663 * .0663 + .01486 * .01486 ) ) . ", d=" .
	($temp_y / sqrt( ( $temp_x * $temp_x ) + ( $temp_y * $temp_y ) ));

$temp_x = $temp_x / sqrt(($temp_x * $temp_x ) + ( $temp_y * $temp_y ) );

$temp_y = $temp_y / sqrt(($temp_x * $temp_x ) + ( $temp_y * $temp_y ) );

echo ", e=" . $temp_y;
?>

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 [2002-11-10 15:48 UTC] derick@php.net
Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.
 [2002-11-10 16:21 UTC] sprice at wisc dot edu
Ummmm.... could you please explain why this isn't an error in PHP? It is only simple math and PHP is giving me an incorrect result.
 [2002-11-10 16:54 UTC] sprice at wisc dot edu
Nope, it isn't a precision problem, it is a regular old PEKAC error or ID 10 T error. Sorry for bothering you.
 
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