Having all the codes in a single file

I saw an example of boundary value problems in the book Numerical Analysis by Sauer. We have the non-linear equation:

The discretized form of this equation :

My question is not about how we solve such a problem. I already have the solution in three files. Ie two functions and a regular matlab file to perform it. I also attached files.I tried to write everything in a single file and wanted to see if it is possible to execute the algorithm without having to write Matlab functions. I did not succeed. Can anyone correct my code?

clc
clear all
n=15;
a=0; b=1; ya=1; yb=4;
h=(b-a)/(n+1);

J=zeros(n,n); %Jacobian
w=zeros(n,1);
y=zeros(n,1);
y(1)=ya-(2+h^2)*w(1)+h^2*w(1)^2+w(2); %BV
y(n)=w(n-1)-(2+h^2)*w(n)+(h^2)*(w(n)^2)+yb; %BV
for i=2:n-1
    y(i)=w(i-1)-(2+h^2)*w(i)+(h^2)*(w(i)^2)+w(i+1);
end


for i=1:n-1
    J(i,i+1)=1;
    J(i+1,i)=1;
end

%The Matrix
for i=1:n
    J(i,i)=2*h^2*w(i)-2-h^2;
end

%The solution!
w=w-J\y;


Y=[1;w;4];
plot(x,Y)
grid on

This is the True solution! but I dont get this plot!

[Jan]

Please explaein, what "I did not succeed" means. Solving a problem is easier than guessing, what the problem is.

[Pouyan Msgn]

I dont get the correct plot with my own code

[Jan]

I do not get any output from your code at all, because x is not defined in the command plot(x,Y).