Why do I have an error on line 17 of the code? or there is another error

syms x
f=x.^8-7*x.^3 + 7;
d=diff(f);
fplot(f,[0 10]);
pause(1);
hold on;
lambda=1;
xo=1;
fxo=1;
x_value=[];
y_value=[];
for i=1:50
    x_value=[x_value xo];
    y_value=[y_value fxo];
    xo=xo-lambda*d;
    fxo=xo.^8-7*xo.^3+7; % Corrección aquí
    plot(x_value,y_value,'*','linewidth',1);
    pause(0.02)
end

Error using plot
Data must be numeric, datetime, duration, categorical, or an array convertible to double.

toc

[Dyuman Joshi]

xo=xo-lambda*d;

What is this line suppossed to do?

xo and lambda are numbers, but d is an expression in the symbolic variable x.

[Freddy]

I try to capture the gradient descent method and that line iterates the values until the minimum is found.

Answer 1

[Walter Roberson]

syms x
f=x.^8-7*x.^3 + 7;
d=diff(f);

d is a symbolic expression in x

    xo=xo-lambda*d;

That symbolic expression in x is used. Note that you are not evaluating d at the current point, so the result is going to involve the symbolic variable x, so you will not be able to convert the result to numeric form.