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About floor function problem.

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C Zeng
C Zeng 2012-10-23
floor(1.999999999999)=1 floor(1.99999999999999999999999999)=2, why is that?
Floor should return the lower integer right? Thanks.

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Matt J
Matt J 2012-10-23
编辑：Matt J 2012-10-23
If that confuses you, this probably will too:
>> isequal(1.99999999999999999999999999, 2)
ans =
1
Anyway, it has nothing to do with the FLOOR command. It's because your big long decimal can't be distinguished from 2 in floating point.
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Matt J
Matt J 2012-10-23
What was your "previous question"?

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Azzi Abdelmalek
Azzi Abdelmalek 2012-10-23
Just try without floor
a=1.99999999999999999999999999
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Walter Roberson
Walter Roberson 2012-10-23
If you are starting with an integer, then dividing by a power of 2 can never result in this kind of round-off. Powers of 2 are represented exactly in binary floating point numbers, and dividing by a power of two effectively only changes the internal binary exponent without changing the mantissa. If you are running into this kind of round-off then either you are not starting with an integer or you are not dividing by a power of 2.
C Zeng
C Zeng 2012-10-26
Thanks, Walter, though I do not understand your point. I am transferring an integer like N to 2-digits. I want to divide it by 2 to determine if the entry is 0 or 1. Floor function does not make sufficient proximity to this problem.

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