dx=2;
dt=1;
x=[0:dx:10];
n=length(x);
lambda=0.020875;
%initializa IC & BC
for k=1:n
T(k,1)=0;
T(k,2)=0;
end
T(1,1)=100;
T(1,2)=100;
T(6,1)=50;
T(6,2)=50;

A=zeros(n-2,n-2);
B=zeros(n-2,1);

for k=1:n-2
A(k,k)=2*(1+lambda);

if k==1
%don't do left of diagonal
B(k,1)=lambda*T(k+2,1)+2*(1+lambda)*T(k+1,1)+lambda*T(k,1)+lambda*T(k,k+1);
else
A(k,k-1)=-lambda;
end

if k==n-2
%don't do right of diagonal
B(k,1)=lambda*T(k+2,1)+2*(1+lambda)*T(k+1,1)+lambda*T(k,1)+lambda*T(k+2,2);
else
A(k,k+1)=-lambda;
end

end