How to evaluate a function that has been saved to a variable
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I have a function:
f = @(x) 2*tanh(x/2)
I'm taking the 1,2,3 derivatives of
d1 = diff(f(x))
d2 = diff(f(x),2)
d3 = diff(f(x),3)
I want to plot them now but not sure how to do this. If I try the following it gives me an error:
x = -1:0.01:1;
plot(x, d1(x))
How do you plot them if they are stored in a variable? or evaluate them?
2 个评论
Adam Danz
2021-5-13
> How do you plot them if they are stored in a variable? or evaluate them?
Your example uses values stored in a variable so I'm not sure what you're asking.
Don't forget that d1 will have 1 less value than x since you're differentiating, d2 will have 2 less values, etc.
采纳的回答
Walter Roberson
2021-5-13
%provided that x is symbolic
d1(x) = diff(f(x))
d2(x) = diff(f(x),2)
d3(x) = diff(f(x),3)
2 个评论
Eth
2021-5-13
f = @(x) 2*tanh(x/2)
syms x
d1(x) = diff(f(x))
d2(x) = diff(f(x),2)
d3(x) = diff(f(x),3)
simplify(d2(2))
Looks fine to me.
If you are expecting decimal values, then use vpa()
更多回答（1 个）
David Hill
2021-5-13
syms x;
f = 2*tanh(x/2);
d1 = diff(f);
d2 = diff(f,2);
d3 = diff(f,3);
fplot(f,[-1,1]);
hold on;
fplot(d1,[-1,1]);
fplot(d2,[-1,1]);
fplot(d3,[-1,1]);
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