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The code does not work with 1.7

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net
net 2011-11-30
This code works normally accept 1.7
it does not count 1.7
I coul not understand why
y=[1.3,1.3,1.7,1.3,1.7,1.6,1.8,1.9,1.6]; %y=[1.7,1.7,1.7,1.7,1.7,1.7,1.7,1.7,1.7]; x=1;
for i=1:0.1:1.9
v(x)=sum(y==i);
x=x+1;
end
v
  2 个评论
Wayne King
Wayne King 2011-11-30
what are you trying to do with this code???
net
net 2011-11-30
I wanted to count elements.
1.3 => 3 times
1.7 => 2 times etc.
These answers solved my problem.
Thanks for the all of answers.

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采纳的回答

Titus Edelhofer
Titus Edelhofer 2011-11-30
Hi,
this is due to roundoff: 0.1 is not representable as a finite number in binary system. Note the following:
i=1:0.1:1.9;
i(9)-1.8
ans =
-2.2204e-016
And then your test on equality fails ...
Titus

更多回答（3 个）

Robert Cumming
Robert Cumming 2011-11-30
As said above you have encountered the problem of floating point arithmetic, if change your counter to be 1 instead of 0.1 (and change your inner the line to:
v = sum (y==i/10)
you will see 1.7 is counted.
Its worth understanding that computer are not exact due to the way they store information in memory, for example try:
[0.3-0.2 == 0.1]
[0.3-0.2-0.1]
They answers are not what you might expect... Note this is not a problem of Matlab alone. Have a read of this answer
Junaid
Junaid 2011-11-30
Anyway you can do what ever you want from this simple one lines.
v =hist(y,[1:.1:2])
This is simple. Take the histgram. The number of bins are decided by [1:.1:2].
net
net 2011-11-30
Thanks for the answers.

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