function Problem24p14
% Coded by NFR on 12.1.2016
% This code solves the film diffusion problem
%
e = ones(1,12);
e(1) = 0;
f = ones(1,12)*-2;
f(12) = -1;
g = ones(1,12);
g(12) = 0;
r = zeros(1,12);
r(1) = -.1;
C_vec = Tridiag(e,f,g,r);
C_vec = [100 C_vec];
X_vec = [0:1:12];
plot(X_vec,C_vec)

end

function x = Tridiag(e,f,g,r)
% Tridiag: Tridiagonal equation solver banded system
% x = Tridiag(e,f,g,r): Tridiagonal system solver.
% input:
% e = subdiagonal vector
% f = diagonal vector
% g = superdiagonal vector
% r = right hand side vector
% output:
% x = solution vector
n=length(f);
% forward elimination
for k = 2:n
factor = e(k)/f(k-1);
f(k) = f(k) - factor*g(k-1);
r(k) = r(k) - factor*r(k-1);
end
% back substitution
x(n) = r(n)/f(n);
for k = n-1:-1:1
x(k) = (r(k)-g(k)*x(k+1))/f(k);
end
end