Why loop is not being excluded with the given condition?

I am using the continue function to exclude the nodes of a sine function in matlab. When I start from 0, it is excluding all the nodes. However, when I start from 0.1 (for some reasons), it does not exclude the nodes i.e. 1.5, 2.5, 3, 3.5. Can you tell me what can be the reason and how to deal with it?

F_b = 16000; % N
A_b = 125.66; % mm^2
for cycles = 0:0.1:10
    if cycles/0.5 == fix(cycles/0.5)
        continue
    end
    disp(cycles)
end

    0.1000

    0.2000

    0.3000

    0.4000

    0.6000

    0.7000

    0.8000

    0.9000

    1.1000

    1.2000

    1.3000

    1.4000

    1.6000

    1.7000

    1.8000

    1.9000

    2.1000

    2.2000

    2.3000

    2.4000

    2.6000

    2.7000

    2.8000

    2.9000

    3.1000

    3.2000

    3.3000

    3.4000

    3.6000

    3.7000

    3.8000

    3.9000

    4.1000

    4.2000

    4.3000

    4.4000

    4.6000

    4.7000

    4.8000

    4.9000

    5.1000

    5.2000

    5.3000

    5.4000

    5.6000

    5.7000

    5.8000

    5.9000

    6.1000

    6.2000

    6.3000

    6.4000

    6.6000

    6.7000

    6.8000

    6.9000

    7.1000

    7.2000

    7.3000

    7.4000

    7.6000

    7.7000

    7.8000

    7.9000

    8.1000

    8.2000

    8.3000

    8.4000

    8.6000

    8.7000

    8.8000

    8.9000

    9.1000

    9.2000

    9.3000

    9.4000

    9.6000

    9.7000

    9.8000

    9.9000

The other is

F_b = 16000; % N
A_b = 125.66; % mm^2
for cycles = 0.1:0.1:10
    if cycles/0.5 == fix(cycles/0.5)
        continue
    end
    disp(cycles)
end

    0.1000

    0.2000

    0.3000

    0.4000

    0.6000

    0.7000

    0.8000

    0.9000

    1.1000

    1.2000

    1.3000

    1.4000

    1.5000

    1.6000

    1.7000

    1.8000

    1.9000

    2.1000

    2.2000

    2.3000

    2.4000

    2.5000

    2.6000

    2.7000

    2.8000

    2.9000

    3.0000

    3.1000

    3.2000

    3.3000

    3.4000

    3.5000

    3.6000

    3.7000

    3.8000

    3.9000

    4.1000

    4.2000

    4.3000

    4.4000

    4.6000

    4.7000

    4.8000

    4.9000

    5.1000

    5.2000

    5.3000

    5.4000

    5.6000

    5.7000

    5.8000

    5.9000

    6.1000

    6.2000

    6.3000

    6.4000

    6.6000

    6.7000

    6.8000

    6.9000

    7.1000

    7.2000

    7.3000

    7.4000

    7.6000

    7.7000

    7.8000

    7.9000

    8.1000

    8.2000

    8.3000

    8.4000

    8.6000

    8.7000

    8.8000

    8.9000

    9.1000

    9.2000

    9.3000

    9.4000

    9.6000

    9.7000

    9.8000

    9.9000

Thanks for the help in advance.

Regards,

Muhammad Hassaan Bin Tariq

[Stephen23]

"Can you tell me what can be the reason..."

Because 0.1 cannot be exactly stored in a binary floating point number (in exactly the same way that you cannot write 1/3 exactly on a piece of paper using a decimal fraction). The floating point error accumulates differently in the COLON operator, depending on the provided values. Lets compare:

cycles0 =   0:0.1:10;
cycles1 = 0.1:0.1:10;
fprintf('%.40f\n', cycles0(16)/0.5, fix(cycles0(16)/0.5), cycles1(15)/0.5, fix(cycles1(15)/0.5))

3.0000000000000000000000000000000000000000
3.0000000000000000000000000000000000000000
3.0000000000000004440892098500626161694527
3.0000000000000000000000000000000000000000

"...and how to deal with it?"

Either:

• work with integers, or
• use tolerances when comparing (i.e. do not use exact equality), avoid FIX, etc.

Your current approach is numerically fragile and should be avoided.

[Muhammad Hassaan Bin Tariq]

I got your point but why is it avoiding higher points with the same fix command? I mean it is excluding 7, 7.5, 8 etc.

It is a long code. Well the mod() operation is working well.

Thanks for your help very much.

Regards

Answer 1

[Tobias Panitz]

Hey,

have you tried using the modulus function?

Remainder after division (modulo operation) - MATLAB mod - MathWorks Deutschland

if mod(cycles,0.5) == 0
    continue;
end