Equation is correct but logically false???

Hi all,

I can´t make any sense of this. I have this very simple equation that is equal to 0.1 according to Matlab itself. Yet when I try to create an if statement where something happens if the value is equal to 0.1 Matlab tells me the statement is logically false:

>> a = 11

a =

      11

>> (a/10)-(floor(a/10))

ans =

      0.1000

>> (a/10)-(floor(a/10))==0.1

ans =

    logical

     0

Even weirder, it works fine when the equation equals another number like 0.6 or 0.7 (but not 0.2 or 0.3).

Any help understanding this would be very welcome!

[Stephen23]

"Any help understanding this would be very welcome!"

You should read this:

https://orion.math.iastate.edu/alex/502/doc/p5-goldberg.pdf

And any of the one million threads on this forum where floating-point numbers are discussed:

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

https://www.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

https://www.mathworks.com/matlabcentral/answers/321709-strange-behaviour-of-matlab-find-command

https://www.mathworks.com/matlabcentral/answers/329124-how-does-6-022140857-10-23-differ-from-6-022140857e-23

[Florent Dueme]

Thanks a lot for the links and sorry for the boring question! Wasn´t sure what to look for as I didn´t know it was a floating-point numbers issue.

Answer 1

[Star Strider]

This is one of the better discussions on the problem you are experiencing: Why is 0.3 - 0.2 - 0.1 (or similar) not equal to zero? (link).

[Florent Dueme]

Thanks!

[Star Strider]

My pleasure!