Unexpected computation result

Question

Here is my whole function:

function val = deceptive_3_nd_function( arr )
    alpha = [0.3 0.7];
    beta = 0.2;

    val = zeros(size(arr,1),1);
    for part=1:size(arr,1)
        for i=1:size(arr,2)
            if 0 <= arr(part, i) && arr(part, i) <= 4/5*alpha(i);
                val(part) = val(part) - arr(part, i)/alpha(i) + 4/5;
            elseif 4/5*alpha(i) < arr(part, i) && arr(part, i) <= alpha(i)
                val(part) = val(part) + 5*arr(part, i)/alpha(i) - 4;
            elseif alpha(i) < arr(part, i) && arr(part, i) <= (1+4*alpha(i))/5
*               a_ = 5.0 * ( arr(part, i) - alpha(i) );
*               b_ = alpha(i)-1.0;
*               c_ = a_/b_;
*               val(part) = val(part) + c_ + 1.0;
            elseif (1+4*alpha(i))/5 < arr(part, i) && arr(part, i) <= 1
                val(part) = val(part) + (arr(part, i)-1)/(1-alpha(i)) +4/5;
            end
        end
        val(part) = -(1/size(arr, 2)*val(part))^beta;
    end
end

In lines marked with asterisks in got unexpected results. As you can see I tried to isolate a problem and that's where it led me:

K>> arr(part, i)

ans =

    0.7600

K>> arr(part, i)==0.76

ans =

     1

K>> alpha(i)

ans =

    0.7000

K>> alpha(i)==0.7

ans =

     1

K>> arr(part, i) - alpha(i)

ans =

    0.0600

K>> arr(part, i) - alpha(i) == 0.06

ans =

     0

Why is this happening..?

Answer 1

Looks like you've run into floating point error there.

(0.76 - 0.7) == 0.06
ans =
    0

num2str(0.76 - 0.7, '%0.20f')
ans =
0.06000000000000005300