I dont understand why the variable x is incorrect.

Please explain to me what is wrong!

[John D'Errico]

It is so much easier to help you if you paste in the code itself, instead of a picture of your code. Why would you want to make it more difficult to get help?

[Nam]

N = 1 + randi(15); % define number of zeros to be found, [1 16] 
r = zeros(N,2); % preallocate r vector

% Define the function handles.
syms x;
bessel0 = @(x) besselj(0,x);
bessel1 = @(x) besselj(1,x);

% Set the arguments for FZERO.
options = optimset('Display','none','TolX',1e-8);

% Develop iterative scheme for finding first N zeros of J0
r(1,:) = [bessel1(1)/bessel0(1), bessel0(bessel1(1)/bessel0(1))];
for n = 2:N
    % Use previous extremum location as initial guess for current extremum
    x0 = r(n-1,1) + pi;
    % Find current extremum using fzero
    r(n,:) = [fzero(bessel0, x0, options), 0];
    % Calculate corresponding value of Bessel function for current extremum
    r(n,2) = bessel0(r(n,1));
end
%%%%%  Plot the function and the extrema %%%%%%%%%%.
% Define the x values.
%x = 0:0.1:30; % use this range when you are trying to get a sense of the problem
x = 0:0.1:r(N,1); % use this range when you want to see all your zeros
% make figure
figure; hold on; grid on;
plot(x,bessel0(x),'k')
plot(x,bessel1(x),'Color',[0.6350 0.0780 0.1840])
plot(r(:,1),r(:,2),'o','Color',[0 0.4470 0.7410])
plot(r(:,1),0*r(:,1),'x','Color',[0.4660 0.6740 0.1880])
axis([0 max(x) -1 1]);
legend('Bessel J of Order Zero','Bessel J of Order One','Extrema of Order Zero','Zeros of Order One')

[Walter Roberson]

Question:

What is the purpose of your syms x; line ?

[Nam]

i remove it and the answer is still wrong

Answer 1

[Paul]

Hi Nam,

What is the justification for the computation of r(1,:)?

If you're trying to find the extrema of J0, why use fsolve to find points where J0 = 0?

[Nam]

Hi Paul

What do you suggest? I don't really understand.

[Paul]

I'm afraid I can't be of much more help other than suggesting to reread:

the problem statement and figure out what the condition is for J0 to have an extremum, which will determine what needs to be solved using fsolve, and

reread item 4 to understand how to initialize the solution.