colon operator rounding problem
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Hello everyone!
I encountered a problem in one of my code, using the semi colon operator like this:
a = 0:0.1:120;
will not give me exactly what I want, it does return 0, 0.1, 0.2 etc, but with a small imprecision (equal to eps actually)
the following code :
a = 0:0.1:120;
disp(a(20));
disp(a(20)-1.9)
isequal(a(20),1.9)
is returning:
1.9
2.22044604925031e-16
ans =
0
Any help ? I really need this isequal(a(20),1.9) to return 1...
thanks !
Réponse acceptée
bio lim
le 10 Juil 2015
Try it like this.
a=(0:1200)/10;
disp(a(20));
disp(a(20)-1.9);
isequal(a(20),1.9)
Your previous code was not returning 1 because of rounding errors when doing finite precision arithmetic.
3 commentaires
bio lim
le 10 Juil 2015
Modifié(e) : bio lim
le 10 Juil 2015
If you multiply it by decimals, such as 0.1, again you get rounding errors. That is why, I specifically wrote 10 in the first place. If you actually check your initial code, you can see that until a(4), it returns 0 but starts getting rounding error from that point.
1/0.1 returns 10 because, 1 is defined and when you divide you are going to get 10 without a rounding error.
Plus de réponses (2)
Steven Lord
le 10 Juil 2015
See question 1 in the Mathematics section of the FAQ for a more detailed explanation of this behavior.
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