Using symbolic gradient with another function

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Braden Kerr
Braden Kerr 2020-11-4
评论： Walter Roberson 2020-11-4
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

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回答（1 个）

Ameer Hamza
Ameer Hamza 2020-11-4
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

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