How do I make my variables save from my function?

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Sarah Johnson
Sarah Johnson 2020-2-19
编辑： Sabin Thapa 2021-2-17
I have written a function function [f, grad, gradTwo] = Rosen(x), which returns the Rosenbrock function value f(x) to f, its gradient vector ∇f(x) to grad, and its Hessian matrix ∇f(x) to gradTwo, at the given input point x and verify the function returns correct values.
I have written a function that does so, using x = [1, 1], but my values don't store.
function [f, grad, gradTwo] = Rosen(x)
g = @(x)100*(x(2) - x(1)^2)^2 + (1 - x(1))^2;
f = g(x);
grad = [-400*(x(2)-x(1)^2)*x(1)-2*(1-x(1)); 200*(x(2)-x(1)^2)];
gradTwo = [800*x(1)+2, -400*x(1); -400*x(2), 200];
end
Then my output when I run this is:
ans =
0
I believe my professor wants it to look like this:
f =
0
grad =
0
0
gradTwo =
802 -400
-400 200
Is there a way to accomplish this? Any advice would be great, I'm not that great at MATLAB
  1 个评论
Sabin Thapa
Sabin Thapa 2021-2-17
编辑：Sabin Thapa 2021-2-17
Hi, if grad = ∇f(x) and gradTwo = ∇^2 f(x), then these should be:
grad = [400*x(1)^3 - 400*x(1)*x(2) + 2*x(1) - 2; 200*(x(2)-x(1)^2)];
and gradTwo = [1200*x(1)^2 - 400*x(2) + 2, -400*x(1); -400*x(1), 200];
(related to mathematics, not coding)

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采纳的回答

Hiro Yoshino
Hiro Yoshino 2020-2-19
You're doing well!
Try this:
x = [1 1];
[f, grad, gradTwo] = Rosen(x)
You should prepare the three variables that recieve the calculus!

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