As per my understanding,you are encountering an error while trying to plot the roots of Wilkinson polynomial.In this case,the potential cause behind the error is that you are not specifying the X-Values for the polynomial.
Please refer below for the corrected version of code.
syms x;
n = 20;
P20 = prod(x-(1:n));
P = expand(P20);
z = roots(P);
fmt = '%25.16f\n';
fprintf(fmt,z);
% Evaluate the polynomial at 1000 points between -1.5 and 1.5
x_vals = linspace(-1.5, 1.5, 1000);
y_vals = subs(P, x_vals);
% Plot the polynomial and the roots
figure;
plot(x_vals, y_vals);
I hope the provided resolution helps!
