solve_tridiag.m

function x=solve_tridiag(ud,uo,lo,b);```
  % solve_tridiag solves Ax=b  for x
  % given 
  % the diagonal of the Upper matrix, ud
  % the off-diagonal of the Upper matrix, uo
  % the off-diagonal of the Lower matrix, lo
  % the vector b
  % note: the diagonal of the Lower matrix is all ones

end