[Scilab-users] Help me plot y = x^(1/3);

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lepezhr lepezhr
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[Scilab-users] Help me plot y = x^(1/3);

I have problems to graph the function

x=[-10:1:10]

y = x^(1/3);

plot(x,y);

the same in plot of google gives a graph but scilab does anything with the sign.

Héctor Lépez

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Denis Crété Denis Crété
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Re: Help me plot y = x^(1/3);

Hello,

 

The operator ^ seems to return the real part of one of the complex roots of x^3=1.

If x=[-10:1:10]
and
y = x^(1/3);
Thus, for x<0, the values of y are half the opposite of values obtained with x>0.

With y=x.^(1/3), the values of y are complex for x<0.

HTH

Denis

De : users [mailto:[hidden email]] De la part de Hector R. Lepez
Envoyé : vendredi 9 mars 2018 11:58
À : [hidden email]
Objet : [Scilab-users] Help me plot y = x^(1/3);

 

I have problems to graph the function


x=[-10:1:10]

y = x^(1/3);

plot(x,y);

the same in plot of google gives a graph but scilab does anything with the sign.

 

Héctor Lépez


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Denis Crété
mottelet mottelet
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Re: Help me plot y = x^(1/3);

In reply to this post by lepezhr
Le 09/03/2018 à 11:57, Hector R. Lepez a écrit :
I have problems to graph the function

x=[-10:1:10]

y = x^(1/3);

plot(x,y);

the same in plot of google gives a graph but scilab does anything with the sign.

Héctor Lépez


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[hidden email]
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By default in scilab non-integer power elevation of negative number is made in the complex domain. The particular case of the real cubic root can be treated like this :

y = sign(x).*abs(x)^(1/3);

otherwise (-1)^(1/3) gives you one of the complex cubic root of -1, namely exp(%i*%pi*1/3)

S.

-- 
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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lepezhr lepezhr
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Re: Help me plot y = x^(1/3);

This solution worked, could you explain how you put it together? What does it mean to put a sign (x) * ?? Thank you


Héctor Lépez Cel: 154137337


El viernes, 9 de marzo de 2018 09:25:18 ART, Stéphane Mottelet <[hidden email]> escribió:


Le 09/03/2018 à 11:57, Hector R. Lepez a écrit :
I have problems to graph the function

x=[-10:1:10]

y = x^(1/3);

plot(x,y);

the same in plot of google gives a graph but scilab does anything with the sign.

Héctor Lépez


_______________________________________________
users mailing list
[hidden email]
http://lists.scilab.org/mailman/listinfo/users

By default in scilab non-integer power elevation of negative number is made in the complex domain. The particular case of the real cubic root can be treated like this :

y = sign(x).*abs(x)^(1/3);

otherwise (-1)^(1/3) gives you one of the complex cubic root of -1, namely exp(%i*%pi*1/3)

S.

-- 
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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[hidden email]
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Christophe Dang Ngoc Chan Christophe Dang Ngoc Chan
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Re: Help me plot y = x^(1/3);

In reply to this post by lepezhr
Hello Hector,

> De : Hector R. Lepez
> Envoyé : vendredi 9 mars 2018 13:58
>
> What does it mean to put a sign (x) * ??

You'll find some answers here:

https://help.scilab.org/docs/6.0.1/en_US/sign.html

https://help.scilab.org/docs/6.0.1/en_US/hat.html

https://help.scilab.org/docs/6.0.1/en_US/dot.html

Regards

--
Christophe Dang Ngoc Chan
Mechanical calculation engineer
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