Beefy Boxes and Bandwidth Generously Provided by pair Networks
go ahead... be a heretic
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
This is a usual difficulty with floating point number arithmetics (with most languages). In your first example, try this:
my $x = 0.95*806; my $y = 1.3*589; print $y - $x; # prints something like : 1.13686837721616e-13
So, although the numbers seem to be equal when rounded to 1 or even 5 decimal places, they are not really equal. Even if the numbers were mathematically exactly equal, the simple fact that you derived them from arithmetical operations on other source floating point numbers may lead to different results, because the original numbers are first converted to an internal binary representation which may lead to some internal rounding even before the multiplication is applied.

The lesson is: don't compare for equality floating point numbers derived from arithmetic operations; rather subtract one from the other and check if the absolute value of the difference is smaller than a certain predetermined very small number.


In reply to Re: Comparing results of math operations by Laurent_R
in thread Comparing results of math operations by stangoesagain

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others surveying the Monastery: (5)
    As of 2014-11-28 01:32 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      My preferred Perl binaries come from:














      Results (191 votes), past polls