Le 13/09/2019 à 15:13, Dang Ngoc Chan, Christophe a écrit :
Hello,
De : Stéphane Mottelet
Envoyé : vendredi 13 septembre 2019 14:23
I think that we do agree about the fact that the actual Scilab display
[...]
--> x(8)
ans =
1.7
--> x(8)-1.7
ans =
2.220D-16
is pretty but not correct/homogeneous/honest
Maybe I was not clear enough.
1.7 cannot be stored exactly in IEEE754 encoding so it should always be
displayed with trailing zeros.
So
--> x(8)-1.7
ans =
2.220D-16
is OK and should always be displayed like this, but the previous display
--> x(8)
ans =
1.7
is not OK. What is not correct/homogeneous/honest is the fact that we have this
both displays in the current version of Scilab.
I don't agree about this.
The decimal number can only rarely be represented exactly in binary according
to IEEE 754.
This means that there should always be trailing zeros to highlight the fact
that there is a 10^-16 discrepancy between the stored value and the displayed
value?
I don't find this convenient.
The fact that some people are not aware of this discrepancy can be a problem
but it is the general problem of underflow or subtractive cancellation or
round-off error etc.
The problem is not less important than ignoring a number is complex with a zero
imaginary part, but I'm not sure it can be handled in the same way.
--
Christophe Dang Ngoc Chan
Mechanical calculation engineer
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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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