0.9-0.89 is 0.01000000​0000000000​2081668171​17217

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john
john 2013-8-15
Hi, why
0.9-0.89 is 0.010000000000000000208166817117217?
I want to use it in:
if a-b<c sprintf('error') end......
when I use vpa, than I get error in if..
thank you

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Image Analyst
Image Analyst 2013-8-15
One of the most frequently asked questions, so see the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
  2 个评论
James Tursa
James Tursa 2013-8-15
@John, For your particular example:
>> num2strexact(0.9)
ans =
0.90000000000000002220446049250313080847263336181640625
>> num2strexact(0.89)
ans =
0.89000000000000001332267629550187848508358001708984375
>> num2strexact(0.9-0.89)
ans =
1.00000000000000088817841970012523233890533447265625e-2
As you can see above, none of the numbers involved can be represented exactly in IEEE double precision floating point. You can find NUM2STREXACT here:
http://www.mathworks.com/matlabcentral/fileexchange/22239-num2strexact-exact-version-of-num2str

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