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Relational Operators Issue - 1 is not equal to 1.000

Asked by usr0815 on 29 May 2012
Hey there,
the following CODE (MATLAB 2011b) results in an unexpected problem, which I'd like to know the reason for:
x = 0;
y = 1;
for i = 1:10
x = x + 0.1;
end
Result:
x = 1.0000
y = 1
The use of some relational operators to compare x and y
a = y == x;
b = y < x;
c = y > x;
Results:
a = 0
b = 0
c = 1
It seems as if the value of x after passing the for-loop is less than 1, even though the workspace displays x = 1.0000... and y = 1.
Actually I experienced this problem in some measurement automation loop and solved it by using
d = y == round(x*100000)/100000;
Result:
d = 1
The question arises: Is this the only/best way to solve this problem or is there a better work-around - maybe a generalized solution - that avoids such problems in advance!
Additional information: Both variables x and y are DOUBLE after the creation.
Thanks for your help!

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1 Answer

Answer by Thomas
on 29 May 2012
 Accepted Answer

  1 Comment

Yes, see that FAQ.
You are only displaying a few digits after the decimal place, and for *display* purposes the value you are displaying rounds to 1.000 but that does not mean that the value *is* 1

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