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why coding this function returns un exact numerical results?

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Cantor Set
Cantor Set 2021 年 6 月 22 日
コメント済み: Walter Roberson 2021 年 6 月 23 日
Ackley's Function (a=20,b=0.2) d=2.
function [ y ] = objfun14 (phen )
d=size(phen,2);
v=cos(2*pi*phen); x=(1/d)* sum(v,2);
t=-20*exp(-0.2*sqrt((1/d)*sum(phen.^2,2))) - exp( x ) +20+exp(1);
y=sum(t,2);
end
%when phen=[0 0] the output should be t=0 however excuting the code gives t=8.8818e-16
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Scott MacKenzie
Scott MacKenzie 2021 年 6 月 22 日
t=8.8818e-16 is pretty close to zero. You are dealing with floating point arithmetic, that's why the result is not exactly what you expect. See Floating-Point Numbers for further details.

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回答 (1 件)

Kishan Dhakan
Kishan Dhakan 2021 年 6 月 23 日
Try using 'format long', which shows 15 decimal places. If it still doesn't work, then your value is probably smaller than what many call 'machine epsilon' and hence is getting rounded to zero.
  1 件のコメント
Walter Roberson
Walter Roberson 2021 年 6 月 23 日
The other way around, the function is returning -4*eps when the user expects 0

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