Differentiating in Matlab

Last lab, we learned how to calculate limits. Basically we started by invoking the symbolic toolbox

syms x

and then defined a corresponding function f that depends on x. For example to create a function f(x) = x^3 we typed

f = x.^3

 
f =
 
x^3
 
 

Now, if we want to calculate the derivative of this function at a symbolic point a, we can do this by using the Matlab command limit:

syms a
fpa = limit((subs(f,x,x)-subs(f,x,a))/(x-a), x,a)

 
fpa =
 
3*a^2
 
 

produces the derivative of f(x) at the point a as being 3a^2.

You can also calculate the derivative using the Matlab command diff. For instance,

dfdx = diff(2*x+x^4)

 
dfdx =
 
2+4*x^3
 
 

will create a function dfdx that contains the derivative 2 + 4x^3. Enjoy!

Published with MATLAB® 7.5