MATLAB Central Newsreader - Very simple number equation does not equate.

Very simple number equation does not equate.

sun — Sun, 05 Jul 2009 15:54:52 -0400

Dear matlab gurus,

I encountered a very puzzling problem. 0.2+0.2+0.2+0.15+0.05 clearly adds up
to 0.8. But on matlab R2007b, it does not equate. Why? I have been tearing
my hair apart as this problem looks so simple and yet elusive. Could some
matlab guru enlighten a newbie like me?

Below are what appears on my matlab screen;

>> 0.2+0.2+0.2+0.15+0.05==0.8

ans =

     0

>> 0.2+0.2+0.2+0.14+0.06==0.8

ans =

     1

>> 0.2+0.2+0.2+0.2==0.8

ans =

     1

Re: Very simple number equation does not equate.

us — Sun, 05 Jul 2009 15:59:02 -0400

"sun" <sun@gmail.com> wrote in message <h2qav3$7um$1@reader01.singnet.com.sg>...
> Dear matlab gurus,
>
> I encountered a very puzzling problem. 0.2+0.2+0.2+0.15+0.05 clearly adds up
> to 0.8. But on matlab R2007b, it does not equate. Why? I have been tearing
> my hair apart as this problem looks so simple and yet elusive. Could some
> matlab guru enlighten a newbie like me?
>
> Below are what appears on my matlab screen;
>
> >> 0.2+0.2+0.2+0.15+0.05==0.8
>
> ans =
>
> 0
>
> >> 0.2+0.2+0.2+0.14+0.06==0.8
>
> ans =
>
> 1
>
>
> >> 0.2+0.2+0.2+0.2==0.8
>
> ans =
>
> 1
>

a hint:

http://matlabwiki.mathworks.com/MATLAB_FAQ#Why_is_0.3-0.2-0.1_not_equal_to_zero_.28or_similar.29.3F

us

Re: Very simple number equation does not equate.

Matt Fig — Sun, 05 Jul 2009 15:59:03 -0400

Congratulations! You are the 1 millionth user to find this same floating point "bug" in MATLAB. See the link below.

http://matlabwiki.mathworks.com/MATLAB_FAQ#Why_is_0.3-0.2-0.1_not_equal_to_zero_.28or_similar.29.3F