how to differentiate a function and then evaluate at a predefined variable?

If i wanted to differentiate f=x*y with respect to y and then evaluate at a value y = 6 say. how would i do this? i would write the code syms y f=x*y g=diff(f) but then how would i go about the evaluation because it seems y is now fixed as a symbol. Also, i have this as predefined input values x,y so i would like to use the y value predefined as i'm writing it in a function

Answer 1

[madhan ravi]

    syms x y

    f=x*y

    A=diff(f,y)

    subs(A,y,6)

[madhan ravi]

If you differentiate f with respect to y the result is x !

[sam plant]

Thank you! I used that example to just keep it simple, my actual equation was involving logs and 3 variables but i just wanted t keep the principle the same. It's working after reading this, i appreciate the help!

[madhan ravi]

Anytime :) , I understood that you needed an example to know the functions , Happy Matlab(ing)