PHP math gets crazy, need explanation, my brain is melting

Posted by derei on Stack Overflow See other posts from Stack Overflow or by derei
Published on 2013-11-05T21:46:51Z Indexed on 2013/11/05 21:53 UTC
Read the original article Hit count: 235

Filed under:

php

|

math

|

floating-point

I know that playing with php float can give strange results if you try to add "goats + apples", but please take a look to the following case:

$val = 1232.81;
$p1  = 1217.16;
$p2  = 15.65;

$sum = $p1 + $p2;
$dif = $val - $sum;

echo $dif;

It will give you -2.2737367544323E-13 ... yeah, ALMOST zero, but then why it doesn't say 0 ? This freaks me out big time. Please, I need some valid explanation.

© Stack Overflow or respective owner

Related posts about php

Magento, NGINX, PHP-FPM, APC, MEMCACHED, 16gb Ram CentOS, Spiking PHP-FPM to 100% CPU

as seen on Server Fault - Search for 'Server Fault'
I have been trying to resolve my issue of spiking cpu caused by php-fpm processes. I've reduced the php-fpm config settings to: pm = ondemand pm.max_children = 12 pm.start_servers = 2 pm.min_spare_servers = 2 pm.max_spare_servers = 10 pm.max_requests = 500 php_admin_value[memory_limit] = 128M Problem… >>> More
PHP Pear Installation on CentOS

as seen on Server Fault - Search for 'Server Fault'
[root@ip ~]# yum install php-pear* Reducing CentOS-5 Testing to included packages only Finished Setting up Install Process Package 1:php-pear-1.8.1-2.el5.centos.noarch already installed and latest versio … >>> More
Apache configurations for php "AddType text/html php" or "AddType application/x-httpd-php php .php"

as seen on Server Fault - Search for 'Server Fault'
I am taking over an application server and discover that it contain the following settings: AddType text/html php Although it works, but my understanding is that it should set as following: AddType application/x-httpd-php php .php What are the key differences between the two settings?… >>> More
mod_rewrite settings causes server to throw HTTP 500 errors instead of 404

as seen on Server Fault - Search for 'Server Fault'
Hello. I have a server with VBulletin forum (working under Apache 2.2, CentOS). The default settings for it in .htaccess are as follows: RewriteEngine on RewriteCond %{HTTP_HOST} ^gsmforum\.ru RewriteRule (.*) http://www.gsmforum.ru/$1 [R=301,L] # If you are having problems or are using VirtualDocumentRoot… >>> More
Problems installing Memcache (PECL extension)

as seen on Server Fault - Search for 'Server Fault'
I have installed memcached fine, and now I will need to install PECL extension memcache. Im running RedHat x86_64 es5. The installation gives me this: downloading memcache-2.2.6.tgz ... Starting to download memcache-2.2.6.tgz (35,957 bytes) ..........done: 35,957 bytes 11 source files, building running:… >>> More

Related posts about math

how to make a function recursive

as seen on Stack Overflow - Search for 'Stack Overflow'
i have this huge function and i am wondering how to make it recursive. i have the base case which should never come true, so it should always go to else and keep calling itself with the variable t increases. any help would be great thanks def draw(x, y, t, planets): if 'Satellites' in planets["Moon"]: … >>> More
Sunrise / set calculations

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to calculate the sunset / rise times using python based on the link provided below. My results done through excel and python do not match the real values. Any ideas on what I could be doing wrong? My Excel sheet can be found under .. http://transpotools.com/sun_time.xls # Created on… >>> More
Android-Java: Constructing a triangle based on Coordinates on a map and your bearing

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi Guys, I'm constructing a geolocation based application and I'm trying to figure out a way to make my application realise when a user is facing the direction of the given location (a particular long / lat co-ord). I've got the math figured, I just have the triangle to construct. //UPDATE So… >>> More
Math.max and Math.min outputting highest and lowest values allowed

as seen on Stack Overflow - Search for 'Stack Overflow'
so I'm trying to make a program that will output the sum, average, and smallest and largest values. I have everything basically figured out except the smallest and largest values are outputting 2147483647 and -2147483647, which I believe are the absolute smallest and largest values that Java will… >>> More
Is Programming == Math?

as seen on Stack Overflow - Search for 'Stack Overflow'
I've heard many times that all programming is really a subset of math. Some suggest that OO, at its roots, is mathematically based. I don't get the connection. Aside from some obvious examples: using induction to prove a recursive algorithm formal correctness proofs functional languages lambda calculus asymptotic… >>> More