MATLAB: Minute error in array causes == to be ineffective

MATLABnumber compare

Hi, I am trying to use an if statement using the == comparator to search an array of numbers. Something like this:
for i = 1:100
     if a == array(i,1)
          % do stuff here
     end
end
Doing this, however, leads to the if statement never being true. When I would expect a and the array value to be equal, the statement is still false, due to a very minute difference of something around the order of 10^-8.
What is causing this very small error and what are some of the workarounds you guys suggest? Alternatively, is there a smarter way to search an array of numbers?

Best Answer

Hi Elliot, this is a reality of dealing with floating point numbers. You could use a tolerance
a = randn(10,1);
for ii = 1:length(a)
  if (abs(a(ii)-0)<1e-6)
        disp('true');
  else
        disp('false');
end
end
For example
    x = 1+1e-7;
    y = 1.000000;
They look the same, but
    abs(x-y)<1e-6
returns a 1 (true)
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