I have an issue with the format of number when i use mean2

1 次查看（过去 30 天）

显示更早的评论

shiraz karray 2016-1-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/265724-i-have-an-issue-with-the-format-of-number-when-i-use-mean2

评论： Walter Roberson 2016-1-29

采纳的回答： Ingrid

Hi i m a new user in matlab. I have a problem when i want to calculate

y=mean2((x-mean2(x))/std2(x))

In fact, i should obtain y=0 , but when i use for example this matrix

x=[10 10 9.2 1;8.33 11.66 29 10;4 10 10 2];

i obtain y=-5.5511e-17! could you help me please

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Ingrid 2016-1-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/265724-i-have-an-issue-with-the-format-of-number-when-i-use-mean2#answer_207826

this is very common to floating point operations and basically y == 0 if you compare it to the eps value. You should never compare directly if a variable is equal to zero for this reason but always use abs(y) < eps

3 个评论
显示 1更早的评论隐藏 1更早的评论

shiraz karray 2016-1-29

Thank you so much for your answer.

Walter Roberson 2016-1-29

There is a whole branch of mathematics that has to do with analyzing how small the "arbitrarily_small_threshold" should be, and how to know when you can stop adding terms from a theoretically infinite series.

The situation is like noticing,

"1/3 = 0.33333, so 2*(1/3) = 0.66666, so 3*(1/3) must = 0.99999 so why isn't that 1.00000?"

请先登录，再进行评论。