[Scilab-users] Certain operations are not expressed as floating point

[Federico Miyara]

Stéphane,

Thanks!

Federico Miyara


On 06/02/2020 04:45, Stéphane Mottelet wrote:
>
> Hello,
>
> This problem is fixed in Scilab 6.1
>
> S.
>
> Le 06/02/2020 à 08:30, Federico Miyara a écrit :
>>
>> Dear all,
>>
>> Trying to implement sine integral from the series, my first attempt
>>
>>         y = 0
>>         N = 30;
>>         for n=0:N
>>             y = y + (-1)^n * x.^(2*n+1)./(2*n+1)./factorial(2*n+1);
>>         end
>>
>> works fine for x<20. Now I want to vectorize it so the plan is to 
>> create a polynomial and then apply horner. The coefficients are
>>
>> coe = (-1).^(0:N)./(1:2:2*N+1)./factorial(1:2:2*N+1)
>>
>> I get
>>
>> coe  =
>>
>>          column 1 to 6
>>
>>    1.  -0.055555555556   0.001666666667  -0.000028344671 
>> 0.000000306192  -0.000000002277
>>
>>          column 7 to 19
>>
>>    0.000000000012  -5.09810915D-14   1.65379838D-16   0.   0. 0.   
>> 0.   0.   0.   0.   0.   0.   0.
>>
>>          column 20 to 31
>>
>>    0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
>>
>> From the 10-th coefficient on, the value seems to be 0. However, 
>> coe(10) yields  9.32044813D-22
>>
>> Actually this is a documented behavior (it is described in hhe format 
>> help page). But I wonder if it is advisable, since it may be confusing.
>>
>> Indeed, it took me some time to discover that the coefficients were 
>> stored as floating point. At the beginning I "believed" what I saw 
>> and started to think which would be the best order of the operations 
>> to avoid too small intermediate values.
>>
>> Is there a reason for that behavior that outweighs the inconvenience 
>> I've mentioned?
>>
>> Regards,
>>
>> Federico Miyra
>>
>>
>>
>> _______________________________________________
>> users mailing list
>> users at lists.scilab.org
>> https://antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/lists.scilab.org/mailman/listinfo/users
> -- 
> 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
>
> _______________________________________________
> users mailing list
> users at lists.scilab.org
> http://lists.scilab.org/mailman/listinfo/users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.scilab.org/pipermail/users/attachments/20200206/72232f88/attachment.htm>