n E Z => sin(n*pi) = -1 ?
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the problem is simple at the first glance. if n is an integer, than sin(n*pi) should be "0". But it gives "-0,999".
isInt = @(n) sin(n*pi);
isInt(100000000000000000000000000000);
I get that the number should be small since the computation doesnt go beyond 10^17, but if I give 5, the result is "6*10^-16". Still, is not "0". How can I overcome this problem? is there a method? I need to solve the problem of "integer". It should be "exact integer". I couldn't find a way to get over it. Do you have any idea?
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Réponses (4)
Steven Lord
le 21 Juil 2022
n = 100000000000000000000000000000;
sinpi(n)
6 commentaires
James Tursa
le 21 Juil 2022
Modifié(e) : James Tursa
le 21 Juil 2022
"Basicly I need a way to calculate formulas beyond the limits of IEEE. which I suppose it is not possible. is it?"
Yes, it is. Use the Symbolic Toolbox as others have already suggested.
That being said, I suspect that your "algorithm", which you haven't discussed or shown us, may be producing garbage if you need 30 or more decimal digits of precision to calculate results. What else is going into this calculation and are you carrying enough precision in every variable to make the result meaningful? Can you post this code?
Stephen23
le 21 Juil 2022
n = sym(100000000000000000000000000000)
sin(n*pi)
1 commentaire
James Tursa
le 21 Juil 2022
Modifié(e) : James Tursa
le 21 Juil 2022
Note that sym( ) here is doing the conversion based on its calculated "intent" of the user, since the actual number that gets passed to sym( ) isn't 100000000000000000000000000000 but something "nearby" as close as IEEE double precision can represent:
n = 100000000000000000000000000000;
fprintf('%30.0f\n',n);
Also, there is another subtle conversion going on in the background. The double precision pi value is converted to its symbolic version based again on its calculated "intent" of the user. That is, here is the actual double precision pi value converted to decimal:
fprintf('%60.55f\n',pi);
But The product n*pi results in a conversion of this to the "exact" symbolic pi before sin( ) is called:
n = sym(n)
n*pi
Personally, I prefer to have these silent conversions made explicit in the code so I don't inadvertently get bit downstream. E.g., I typically would calculate this instead up front and use it downstream so there is no possible ambiguity:
sympi = sym('pi')
KSSV
le 21 Juil 2022
n = vpa(100000000000000000000000000000) ;
vpa(sin(n*pi))
1 commentaire
John D'Errico
le 21 Juil 2022
It is more subtle than you think.
n = vpa(100000000000000000000000000000)
vpa(sin(n*pi))
vpa(sin(n*pi),100)
There is a difference.
David Hill
le 21 Juil 2022
Use symbolics.
function [out] = isInt(n)
n=sym(n);
out=double(sin(n*pi));
end
Call function
o=isInt('10000000000000000000000000000000000000000000000000000000000000000000');
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