Rounding in Matlab (very trivial)

Today is my first day using Matlab. I have been using C++ for last few years. Could someone please explain why FALSE is printed here?

%%Rounding of decimal fractions
x1=0.3
x2=0.1+0.1 + 0.1
test1=(x1==x2) % PRINTS FALSE? WHY?

Answer 1

[Steven Lord]

See question 1 in the Mathematics section of the FAQ.

[Ryan Shrott]

But why does this code print TRUE? It seems arbitrary?

x3=0.5;
x4=0.1+0.1+0.1+0.1+0.1;
test2=(x3==x4);

[Image Analyst]

I suppose for some number combinations it will match all the way out to the umpteenth decimal place and for others it won't. Bottom line: to be robust you need to check non-integer floating point numbers against a tolerance and not for equality.

[Walter Roberson]

It does not have to be intuitive: it depends upon the exact bit pattern and upon the rounding mode that is in effect.

https://en.wikipedia.org/wiki/Rounding#Round_half_to_even