comparing between two identical variables returns logic 0?

clc
clear
n=0:63;
x1=0:7;
x=[x1 x1 x1 x1 x1 x1 x1 x1];
y=((-1).^n).*x;
[msg,N1]=find_period(x);
disp(msg);
[msg,N2]=find_period(y);
disp(msg);

%Taking 1 period of Y
y1=zeros(1,N2);
for i = 1:N2
    y1(i)=y(i);
end


if N1==N2
    fprintf('N1=N2=%d \n', N1);
end

ak=our_fourier_series(x1);
bk=our_fourier_series(y1);

for i =1:4
if (bk(i)==ak(4+i))
    disp('bk=ak-N/2')
end
end
bk(6)==ak(2)
bk(6)
ak(2)

as you can see in the command window bk(6) equals ak(2)

but comparing between them returns logic 0

how is that even possible?

Answer 1

[Stephen23]

"as you can see in the command window bk(6) equals ak(2)"

Nope. Just looking at some floating point values displayed in the command window (or variable viewer, etc.) is not a valid way to determine their exact values (and hence is not valid to decide if they are equal). Those values are certainly not equal, which you will see when you view them at a higher precision, e.g. dowload this:

https://www.mathworks.com/matlabcentral/fileexchange/22239-num2strexact-exact-version-of-num2str

"but comparing between them returns logic 0 how is that even possible?"

Simply because the values are not equal. Read these to know why they are not equal:

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

[Mohamed Salah]

Thanks a lot I rounded them and it worked