[Scilab-users] Evaluating a polynomial on a square matrix

[Federico Miyara]

Stéphane,

Thanks, this is great, the use of eye is the way to go to overcome the 
problem of an earlier suggestion which discarded, for instance, A + 2 
for not being what Horner expects; but A + 2*eye(A) is!

Thanks also for making me aware of the simplified syntax 2*eye() which 
adapts its size to the matrix it is added to, and is also 
computationally more efficient, important especially for very large 
matrices.

Best regards,

Federico Miyara


On 24/09/2019 05:34, Stéphane Mottelet wrote:
>
> Why just not writing Horner's algorithm directly ?
>
> functionout=horner_mat(p, 
> X)a=coeff(p)out=zeros(X);fork=degree(p):-1:0out=out*X+a(k+1)*eye()endendfunction--> 
> a=[1 2;3 4]a = 1. 2.3. 4.--> horner_mat(1+%s-%s^2,a)ans =-5. -8. -12. 
> -17.--> eye() + a - a^2ans =-5. -8. -12. -17.S.
> Le 24/09/2019 à 10:31, Dang Ngoc Chan, Christophe a écrit :
>> Hi,
>>
>> I've got some time this morning (-: so this one seems to work and should be a bit more efficient:
>>
>> // **********
>>
>> P = %s^2 + 2*%s + 3
>>
>> C = coeff(P)
>>
>> n = size(C, "c")
>>
>> if n > 1 then
>>
>>      stringP = "X1 = x; "
>>
>>      for i = 3:n
>>
>>          stringP = stringP+"X"+string(i-1)+" = X"+string(i-2)+"*x; "
>>
>>      end
>>
>> else
>>
>>      stringP = ""
>>
>> end
>>
>> stringP = stringP+"Y = "+string(C(1))
>>
>> for i = 2:n
>>
>>      stringP = stringP+" + "+string(C(i))+"*X"+string(i-1)
>>
>> end
>>
>> deff("[Y] = fctP(x)", stringP)
>>
>> // **********
>>
>> Regards
>>
>> --
>> Christophe Dang Ngoc Chan
>> Mechanical calculation engineer
>>
>>
>> General
>> This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error), please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.
>> _______________________________________________
>> 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



---
El software de antivirus Avast ha analizado este correo electrónico en busca de virus.
https://www.avast.com/antivirus
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.scilab.org/pipermail/users/attachments/20190924/ce8a7a1a/attachment.htm>