Strange issue with if expression, failing to compare two variables properly

Hi I'm having this small snippet, i'm finding values of coordinates as Lx1 and Lx2. they are same but if condition is jumping out to else clause! i've no clue on why its happening am i missing something obvious!

%%

    line1 = [2 5 0 ; 9 1 0 ];
    line2 = [1 1 0  ; 13 13 0];

    line1_vector = ( line1(2,:) - line1(1,:))  / sqrt ( sum((line1(1,:)-line1(2,:) ).^2));
    line2_vector = (line2(2,:) - line2(1,:)) / sqrt ( sum((line2(2,:)-line2(1,:) ).^2));

    matrix_A = [ line1_vector(1:2)'   -1*line2_vector(1:2)'];
    matrix_b = [line2(1,1:2)' - line1(1,1:2)'];

    parameter_matrix = matrix_A\ matrix_b;
    Lz1 = line1(1,3) + parameter_matrix(1)*line1_vector(3)
    Ly1 = line1(1,2) + parameter_matrix(1)*line1_vector(2);
    Lx1 = line1(1,1) + parameter_matrix(1)*line1_vector(1)

    Lz2 = line2(1,3) + parameter_matrix(2)*line2_vector(3)
    Ly2 = line2(1,2) + parameter_matrix(2)*line2_vector(2);
    Lx2 = line2(1,1) + parameter_matrix(2)*line2_vector(1)
    if (Lz1==Lz2)
        if (Lx1==Lx2)
            status =0
        else
            status =1
        end
    end

Answer 1

[Matt J]

I doubt they are the same. Even if they are meant to be the same, there are bound to be small floating point round-off errors making them different. Use a tolerance,

 if abs(Lx1-Lx2)<somethingsmall

[vijay]

yes i did it before posting question but i guess my something small was too small, These issues are very dangerous and hard to trace bugs. with matlab i was supposed to take care of maths and not worry about numerical limits. but guess its not easy to get rid of numerical noise Thanks for quick answer..

Answer 2

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[vijay]

Thanks a lot , I'll try to keep in mind this thing I've already used this "==" so many places, god knows how was it running till now.