syntax errors symbolic to logical

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Chance Anderson 2020-12-4

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评论： Chance Anderson 2020-12-4

I am trying to do a backtracking line search algorithm for a stepest decent problem. This bascial means I need to keep using the gradiant and eventually the hessian alot. But I am trying to compare the operators to be able to compare and I just cant get it. below is my code and a photo of what i am trying to do.

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Answer 1

Walter Roberson 2020-12-4

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You missed the point that

requires that the gradient of f be evaluated at x. You are taking the symbolic gradient of f into gf, but you are not evaluating it at x.

Note: if you have a symbolic gradient gf, then you do not need to re-calculate it every iteration: you can calculate gf once and evaluate gf with the current x at every step.

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Chance Anderson 2020-12-4

hey thanks for the help, im not very good at this and your help is very useful cause.

Chance Anderson 2020-12-4

在 MATLAB Online 中打开

So im sorry to ask again

I tried using this evalualtion at several different points of the code. Am i using it in the wrong context

 
f =
 
-log((x_2/5 - 1)*(x_5/2 - 1)*((2*x_4)/5 - 1)*(x_1/10 - 1)*((3*x_6)/5 - 1)*((3*x_3)/10 - 1)*(x_1^2 - 1)*(x_2^2 - 1)*(x_3^2 - 1)*(x_4^2 - 1)*(x_5^2 - 1)*(x_6^2 - 1))

gf =gradient(f);
subs(gf, [x_1, x_2, x_3, x_4, x_5, x_6], x);
deltax = -1*gf;
a = .3;
b = .8;
t = 1;
inc = 1;
step = 0;
startq = f + a * t * gf.' * deltax;
track = f + a * t * gf.' * deltax;
while startq < track
    
    t = t * B^inc; 
    
    disp(inc);
    inc = inc +1;
    disp(track)
end