a problem about symbolic function diff

syms x(t) y(t); f=x*y; I want get df/dx, how to use command diff? Thank you!

Answer 1

[Star Strider]

You do not get df/dx once you have defined x as x(t). You get the Chain Rule:

dfdx = diff(f)

produces:

dfdx(t) =

D(x)(t)*y(t) + x(t)*D(y)(t)

The command diff(f,x) or diff(f, x(t)) throws an error.

Answer 2

[Lucas Carvalho]

In your case, the independent variable is only t, while x and y are dependent of t. To derive the f function partially in terms of x or y, you will need the fulldiff function:

https://www.mathworks.com/matlabcentral/fileexchange/7174-fulldiff-m