floating point calculation bug?

I'm having a problem in doing simple addition and subtraction with
floating numbers.

Following is the problem.

a = 17.9
b = 16.1
then,
(a - 1.8) == b
gives 0, which means that (a - 1.8) is not equal to 16.1.

If I try following, it is ok.
a = 12.9
b = 11.1
(a - 1.8) == b gives '1'.

It looks like MATLAB has a problem in dealing with decimal places.
Is this known to everyone already?
I thought this kind of problem only happens in MS product...

FYI, I tried following to solve the problem temporarily.

a = 17.9
b = 16.1
then,
round((a - 1.8)*10)/10 == b
gives correct answer, which is '1'.

I'm using Mac OS X (tiger) and MATLAB 7.1. I also tried the above
problems on PC with MATLAB7.0, it has the same problem.

K. Sung
.

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