Equality operator error with exact same value

Question

Glenn Franco Gacal 2022-4-13

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1695760-equality-operator-error-with-exact-same-value

评论： Steven Lord 2022-4-14

I have the following code and it presents a bug:

data = 22.7:0.1:24.2; TEMP(1) = 23.1;
if TEMP(1) == data(5)
    3-2 %this is only sample effect
else
    5-2 %this is only sample effect
end

This outputs

3

But if I use

if TEMP(1) == 23.1
    3-2 %this is only sample effect
else
    5-2 %this is only sample effect
end

This outputs

1

You can see from the "data" matrix that data(5) is 23.1.

What kind of bug is this and how can I avoid this kind of bug in the future? I've tried 2 different PCs with different MATLAB versions and they both have the same problem.

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Answer 1

Steven Lord 2022-4-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1695760-equality-operator-error-with-exact-same-value#answer_942075

This is not a bug. See the section "Avoiding Common Problems with Floating-Point Arithmetic" on this documentation page.

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Glenn Franco Gacal 2022-4-14

Thank you for your clarification and I apologize for this noob dilemma!

Steven Lord 2022-4-14

No need to apologize. You aren't the first person to encounter this behavior (it's a common enough question that our documentation staff created a documentation page for it, after all) and you almost certainly won't be the last.

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