Using symbolic gradient with another function

Hello,

I have a question regarding the use of symbolic gradient.

I have an initial function, shown below, that is a function of two variables, x(1) and x(2).

fun = @(x) -9*x(1) -10*x(2) + theta*(-log(100-x(1)-x(2))-log(x(1))-log(x(2)) - log(50-x(1)+x(2)));

This function takes in x, which is a 2x1 matrix. What I am hoping to do is taking the symbolic gradient of fun and get the output as another 2x1 matrix with the associated equations. Is this possible?

I would like to get a vector that is the following

[%gradient(fun) for x(1); %gradient of fun for x(2)]

I am currently attempting to use the line of code:

grad_fun = @(x) gradient(x,[x(1),x(2)]); 

But it returns an error

I will clarify anthing necessary.

Thank you

Answer 1

[Ameer Hamza]

Symbolic gradient require that you define it as a symbolic expression

syms x [1 2]
syms theta

fun = -9*x(1) -10*x(2) + theta*(-log(100-x(1)-x(2))-log(x(1))-log(x(2)) - log(50-x(1)+x(2)));
d_fun = gradient(fun, x)

Result

>> d_fun
d_fun =
 - theta*(1/(x1 + x2 - 100) - 1/(x2 - x1 + 50) + 1/x1) - 9
- theta*(1/(x2 - x1 + 50) + 1/(x1 + x2 - 100) + 1/x2) - 10

[Braden Kerr]

Is your result, d_fun, a 2x1 matrix or just an output?

[Walter Roberson]

2x1 symbolic matrix