Why loop is not being excluded with the given condition?

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Muhammad Hassaan Bin Tariq
评论： Muhammad Hassaan Bin Tariq 2022-10-18
Ran in:
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
  2 个评论
Stephen23
Stephen23 2022-10-18
Ran in:
"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
Muhammad Hassaan Bin Tariq 2022-10-18
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

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采纳的回答

Tobias Panitz
Tobias Panitz 2022-10-18
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

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