This isn't an issue with ismember but with floating point math in general. Computers can't always add and subtract floating point number precisely, which introduces some rounding errors. Thus, when using "==" or ismember to compare floating point numbers, you run into issues.
Read the example for "Comparing Floating Point Numbers" at https://www.mathworks.com/help/matlab/ref/eq.html
C = 0.5-0.4-0.1
%Should be mathematically equal to 0, right? NOPE! returns -2.7756e-17.
C == 0
Equality returns false.
ismember(C, 0)
ismember returns false.
To fix, you have to see if the values are close enough via some sort of tolerance level.
abs(C-0) < 1E-15
Inequality returns true. C is close enough to 0 to be considered 0.
In your case, don't use ismember. Instead do something like:
A=0.2:0.2:20;
B=5:5:20;
for i=1:100
if any(abs(A(i)-B) < 1E-15)
disp(i)
end
end
