function [u]=convdiff(N,M,tau)
h=1/(N+1);
t=0;
epsilon = 1;
c0 = 10;
%
% condition initiale
%
for i=1:N
  u(i)= ?;
end
%
% remplissage de la matrice  A
%
for i=1:N
  a(i) = ?;
end
for i=1:N-1
  d(i) =  ?;
end
for i=1:N-1
  c(i) =  ?;
end
%
% decomposition LU  A = LU
%
c(1)=c(1)/a(1);
for i=2:N-1
  a(i) = ?;
  c(i) = ?;
end
 a(N) = ?;
%
% schema d'Euler retrograde : A u^n+1 = u^n + tau f^{n+1}
%
for n=1:M
  t=t+tau;
%
% second membre du systeme lineaire u^n + tau f^{n+1}
%
  for i=1:N
     u(i) =  ?;
  end  
%
% resolution du systeme lineaire Ly = u^n + tau f^{n+1}
%
  u(1)= ?;
  for i=1:N-1
    u(i+1) = ?;
  end
%
% resolution du systeme lineaire U u^n+1 = y
%
  u(N) = ?;
  for i=N-1:-1:1
    u(i) = ?;
  end
end
