Buying Algorithms or programming
 

I'd like to ask a question of the experts on this forum. How many of you use the algorithms in libraries for your programming, or do you use algorithms on well known libraries at times? I've heard the libraries algorithms are tested for accuracy, and its much faster to download. Do any of you have any experience with specific libraries? :confused:

For a library example
 

Just as an example for clarity, a library like Numerical Algorithm Group (www.nag.com), where you pay $3000 and can download all the algorithms you want. I heard they are checked for accuracy and done in multiple languages. I'm especially interested in those doing complex mathematics.