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  1. #1
    Regular Coder brad211987's Avatar
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    Sep 2005
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    Strange math output in Java

    Can someone explain why the formula (0.278 * 1.0 * 10) equates to 2.7800000000000002 in java? I have a program that is comparing the result of a dynamic formula in order to validate the result, and this little mismatch is causing quite a few false negatives in my validation. These particular numbers are one of the examples that is causing a problem. Strangely enough, (0.27 * 1.0 * 10) equates to 2.7 as it should.

    I've fixed the issue by ensuring all values are floats, but if anyone could enlighten me on why precision is such an issue here I would appreciate it.
    Last edited by brad211987; 12-19-2008 at 03:31 PM.

  • #2
    God Emperor Fou-Lu's Avatar
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    Sep 2002
    Saskatoon, Saskatchewan
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    It has to do with computational mathematics. I'll have to break out old school notes (or maybe we can wait for JDK since I'm pretty sure he has a masters in mathematics), but I believe its the base conversion that does that. I remember covering this in school.
    Consider 1 / 3 in base 10. There is no calculable answer since you end up with 0.333 repeating. Binary however can represent this number (though offhand I can't recall how to calculate it >.<). On the other hand, base 2 cannot handle 1 / 10, which can be handled in base 10.

    I'll look up some info after and post back (if I remember) :P
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