MATLAB: How to tell if a value is an integer

if statement

I have a for loop and this is an example of an iteration within the loop:
x=725*(77/29)
if x==floor(x)
a=1
else
a=0
end
where i am trying to see if x is an integer. a=1 is true which should apply to this since x=1925 however when I run the code it does a=0. How can i fix this?

Best Answer

"...which should apply to this since x=1925 ..."
Nope. Its actual value is:
>> x = 725*(77/29);
>> fprintf('%.40f\n',x)
1925.0000000000002273736754432320594787597656
The difference is:
>> 1925-x
ans =   -2.27373675443232e-13
Clearly your operations accumulate some floating point error. The answer to your question is: change your algorithm so that you are not checking for exact equality between two binary floating point numbers. For example, check the absolute difference against some suitable tolerance value:
abs(A-B)<tol
Read more about binary floating point numbers:
https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero
https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal
http://www.mathworks.com/matlabcentral/answers/102419-how-do-i-determine-if-the-error-in-my-answer-is-the-result-of-round-off-error-or-a-bug
http://www.mathworks.com/matlabcentral/answers/140656-about-numerical-difficulty-of-equality-comparison-operation-between-two-double-real-numbers-in-matlab
This is worth reading as well:
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
http://faculty.tarleton.edu/agapie/documents/cs_343_arch/papers/1991_Goldberg_FloatingPoint.pdf
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