Equality operator error with exact same value

I have the following code and it presents a bug:

data = 22.7:0.1:24.2; TEMP(1) = 23.1;
if TEMP(1) == data(5)
    3-2 %this is only sample effect
else
    5-2 %this is only sample effect
end

This outputs

3

But if I use

if TEMP(1) == 23.1
    3-2 %this is only sample effect
else
    5-2 %this is only sample effect
end

This outputs

1

You can see from the "data" matrix that data(5) is 23.1.

What kind of bug is this and how can I avoid this kind of bug in the future? I've tried 2 different PCs with different MATLAB versions and they both have the same problem.

Answer 1

[Steven Lord]

This is not a bug. See the section "Avoiding Common Problems with Floating-Point Arithmetic" on this documentation page.

[Glenn Franco Gacal]

Thank you for your clarification and I apologize for this noob dilemma!

[Steven Lord]

No need to apologize. You aren't the first person to encounter this behavior (it's a common enough question that our documentation staff created a documentation page for it, after all) and you almost certainly won't be the last.