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Consider the following code: 

f = @(x) x.^2;

Is it possible to get the derivative of the function handle f as another function handle, without defining a symbolic variable?

Cris Luengo
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Msh
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1 Answers1

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No, to obtain a derivative function you need to use the Symbolic toolbox.

But you can get an approximation (finite difference approximation) by creating a function as follows:

f = @(x) x.^2;
d = 1e-6;
df = @(x) (f(x+d)-f(x))/d;

d here determines precision of the approximation. If you make it too small, you'll end up in the floating-point rounding error domain, so be careful!

Testing:

x = -2:0.01:2;
max(abs(df(x) - 2*x))  % returns 1.0006e-06
Cris Luengo
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    Or even better, use higher order schemes, or at least using a central difference `@(x) (f(x+d)-f(x-d))/(2*d)` - allowing you increased accuracy for the same `d`. This is the correct approach though – Wolfie Feb 08 '19 at 11:26