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how to combine symbolics and if statement?

18 vues (au cours des 30 derniers jours)
Karthik Nimishakavi
Karthik Nimishakavi le 15 Oct 2016
Modifié(e) : Karan Gill le 17 Oct 2017
Hello, My function is like this
y=x+2 for 0<=x<=10
y = x^2 for 10<x<=500 and x belongs to 0,500.
so I tried like this
syms x
if x>=0 && x<=10
y=x+2
else y=x^2
end
but i am getting an error saying
"Conversion to logical from sym is not possible"
"Operands to the || and && operators must be convertible to logical scalar values".
Please help me how to overcome this.

Réponse acceptée

Walter Roberson
Walter Roberson le 15 Oct 2016
You cannot use if together with symbolic expressions.
You should be considering using numeric expressions together with logical indexing. See though http://www.mathworks.com/matlabcentral/answers/301165-ode-suite-for-solving-switched-systems#comment_397941 for a discussion on hidden problems with one way of coding that.
You could also code the obscure
evalin(symengine, 'piecewise([0 <= x and x <= 10, x+2], [10 < x and x <= 500, x^2])')
but you will find that it probably will not be of any use to you.

Plus de réponses (1)

Karan Gill
Karan Gill le 20 Oct 2016
Modifié(e) : Karan Gill le 17 Oct 2017
Piecewise is available starting 16b: <http://www.mathworks.com/help/symbolic/piecewise.html>
In this case:
syms y(x)
y(x) = piecewise(0<=x<=10, x+2, 10<x<=500, x^2);
Now try
y(1)
ans =
3
>> y(12)
ans =
144
  1 commentaire
Walter Roberson
Walter Roberson le 20 Oct 2016
Thanks, Karan, I had missed seeing that.

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