issue in find variable

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Muhammad Usman Gul 2020-7-22

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关闭： MATLAB Answer Bot 2021-8-20

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Muhammad Usman Gul 2020-7-22

Please explain to me why it gives me an empty matrix? Out of 100 only following 25 thresholds are also gives empty matrix

0.0600, 0.0700, 0.1000, 0.1500, 0.1800, 0.2100, 0.2400, 0.2900, 0.3500, 0.3600, 0.4100, 0.4200, 0.4700, 0.4800, 0.5700, 0.5800, 0.6900, 0.7000, 0.7100, 0.8200, 0.8300, 0.8400, 0.9400, 0.9500, 0.9600

Stephen23 2020-7-22

编辑：Stephen23 2020-7-22

"Please explain to me why it gives me an empty matrix?"

Read about the behaviors of binary floating point numbers:

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal

http://www.mathworks.com/matlabcentral/answers/102419-how-do-i-determine-if-the-error-in-my-answer-is-the-result-of-round-off-error-or-a-bug

http://www.mathworks.com/matlabcentral/answers/140656-about-numerical-difficulty-of-equality-comparison-operation-between-two-double-real-numbers-in-matlab

This is worth reading as well:

https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

http://faculty.tarleton.edu/agapie/documents/cs_343_arch/papers/1991_Goldberg_FloatingPoint.pdf

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Answer 1

Fangjun Jiang 2020-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/568983-issue-in-find-variable#answer_469323

编辑：Fangjun Jiang 2020-7-22

在 MATLAB Online 中打开

floating point data precision issue. Below is an example, a and b are not equal even though all the visible digits are the same.

>> format long
>> a=1-1/3
a =
   0.666666666666667
>> b=2/3
b =
   0.666666666666667
>> a==b
ans =
  logical
   0
>> abs(a-b)<=eps
ans =
  logical
   1