How can I plot a sym variable?

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Kavan
Kavan 2013-3-4
I am trying to plot a function and it's derivative, but
syms x y
y=4*x*cos(x)+2*x^cos(x^2)
dydx=diff(y)
plot(y)
gives me an error that I cannot convert double to sym. I know I can plot a function and its derivative using LINSPACE but I want the analytical derivative value as well. How can I plot y and dydx? I also know I can use "EZPLOT" but that doesn't let me do very much with the plotter. Is it possible to plot a symbolic variable and if it is now, how do I get an analytical derivative AND plot it in MatLab?
  1 个评论
Walter Roberson
Walter Roberson 2013-3-4
The analytic derivative will be a formula, and you cannot plot() a formula. You could put the formula up as text using text()

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Youssef Khmou
Youssef Khmou 2013-3-4
hi did you try this :
syms x y dy
y=4*x*cos(x)+2*x^cos(x^2)
dy=diff(y,1);
figure, ezplot(y); hold on; ezplot(dy);
  2 个评论
Kavan
Kavan 2013-3-4
yes, but I don't want to use EZPLOT because I can't change the color of the plot
Youssef Khmou
Youssef Khmou 2013-3-4
and if you move back to numeric ? fine ?
xAxis=[0:0.1:10];
Y=subs(y,xAxis);
DY=subs(dy,xAxis);
figure, plot(Y), hold on, plot(DY,'r')

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