I think it would be interesting to include an input argument check in
some functions prone to give complex results in limiting cases (such as
acos or asin) so that if inside the domain (to within 1 %eps) where the
output argument should be real the imaginary part is canceled. Something
like this for scalars:
function y=acos1(x)
if isreal(x)
if -1<=x & x<=1
y = real(acos(x))
else
y = acos(x)
end
end
endfunction
However, I must say that acos(1-%eps) gives on my Scilab 6.0.1 (Windows
7, i7 processor) a result of
0.000000021073424255447,
being %eps
0.0000000000000002220446
I get no imaginary part. I guess there must be some dependency on the
arithmetic engine.
Federico Miyara
On 29/01/2019 12:58, Stéphane Mottelet wrote:
It is the same if x is slightly > 1:
--> x=1+%eps
x =
1.
--> acos(x)
ans =
2.107D-08i
--> format(25); x
x =
1.0000000000000002220446
Le 29/01/2019 à 16:55, Carrico, Paul a écrit :
When I scroll to the list, the lowest (positive) value is 8.4^E -08
(works fine) and no %eps .
How Can I check if %eps is in?
*De :*users [mailto:users-boun...@lists.scilab.org] *De la part de*
Stéphane Mottelet
*Envoyé :* mardi 29 janvier 2019 16:50
*À :* users@lists.scilab.org
*Objet :* [EXTERNAL] Re: [Scilab-users] acos leads to complex values
Le 29/01/2019 à 16:45, Carrico, Paul a écrit :
Dear All
I spent some time in looking for a mistake in my code ; finally
I’ve found that the ACOS of a real vector leads to some complex
values (???)
acos(Scar_P(:,1)./CM_x_CN(:,1))
Are your really sure, because we may have
--> x=-1-%eps
x =
-1.
--> acos(x)
ans =
3.1415927 - 2.107D-08i
S.
(the formula worked so far)
I checked that the input values are correct:
-Comprised between [-1; 1] using MIN and MAX
-Composed only of real values using ISREAL (all the vectors are
correct)
Thus I do not understand why complex values appear ?
May it come from the vectorization ?
Paul
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Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
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Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet
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