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

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shiraz karray
shiraz karray on 29 Jan 2016
Commented: Walter Roberson on 29 Jan 2016
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

Accepted Answer

Ingrid
Ingrid on 29 Jan 2016
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 Comments
Walter Roberson
Walter Roberson on 29 Jan 2016
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?"

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