Re^2: Is this odd behavior a floating point problem? by wickedjester (Initiate) on Mar 23, 2012 at 17:10 UTC 
Yes, I've seen and skimmed this document, but, not to be rude, but I'm not interested in becoming a computer scientist in order to write a script to do basic math. Adding together 0.001 40 times is pretty basic and if my calculator can do it, I not sure I understand why Perl won't.  [reply] 

It's not a Perl problem, it's the problem of representing a nonterminating series for base 2 using a finite number of binary digits. You are accustomed to seeing it in base ten when you try to represent 1/3rd, yet I hear no complaints that your ten counting fingers are malfunctioning. Your calculator gets it right by rounding to the eight or ten significant digits that you see on its little LCD display. In other words, it really doesn't get it right; it just covers up the ugliness. And, in fact, I see a nearly identical question every day in reference to C, C++, PHP, and myriad other programming languages over on StackOverflow. It's not a problem unique to Perl.
I understand that the "What every computer scientist should know..." article is a little beyond what someone who just wants to get the job done might want to digest. That's fine, the article goes into painful details. Try this response (shameless plug, I wrote it), which tries to spell it out in less technical terms: Re: shocking imprecision.
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Yes, I've seen and skimmed this document, but, not to be rude, but I'm not interested in becoming a computer scientist in order to write a script to do basic math. Adding together 0.001 40 times is pretty basic and if my calculator can do it, I not sure I understand why Perl won't.
:) Try site:perlmonks.org What Every Computer Scientist Should Know About FloatingPoint Arithmetic and you can learn from others who weren't satisfied with that document
Now you say you're studying chemical diffusion so I assume you would have heard of significant figures? Surely your professor, when discussing significant figures, would have explained the basic limitations of adding machines (calculators/computers)?
I was hoping, after reading that document, you would ask explicitly how to round numbers for display purposes in perl.
While you can create a calculator using perl (like Tk::Calculator::RPN::HP ), and expect it to do rounding like your pocket calculator, perl itself, not being a calculator, won't hide the details of floating point arithmetic from you, so it is good knowledge to have.
Any scientist using computers for calculations needs to know the limits of his tools.
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say scalar(@arr); # 40
say $#arr; # 39
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