Two dependent switch on float in a loop.

for t=0.2:0.1:4
    fcn(t);
end

function fcn(t)
for x=1:3
    fcn1(x,t)
end
end

function fcn1(x,t)
switch t
    case 0.2
        y=3;
    case 0.3 % why is this skipped when t = 0.3?
        y=2;
    case 0.4
        y=1;
    otherwise
        error('t out of range');
end
switch y
    case 1
        z=1;
    case 2
        z=2;
    case 3
        z=3;
    otherwise
        error('y out of range');
end
z = z+x;
end

What's going on when t = 0.3? The switch case misjudges?

Answer 1

[Jan]

Wow, the most frequently asked question again.

Please read FAQ: why is 0.3-0.2-0.1 not equal 0 .

 why is this skipped when t = 0.3

Because t is not 0.3 . You see that Matlab is convinced, that this case does not happen. Try it:

0.2 + 0.1 - 0.3
% >> 5.55111512312578e-17

Decimal numbers do not have an exact representation in the binary IEEE754 format, which is used for computations in Matlab and otehr programming languages. Therefore you get rounding effects due to the limited precision. See also:

1e17 + 1 - 1e17

When you want to perform numerical computations, it is very essential, that you understand what happens here and therefore this topic is handled in the first lesson and in the first chapter of books about numerics.