Modular Invariant Partition Functions and Method of Shift Vector

Using shift vector method we obtain a large class of self-dual lattices of dimension $(l,l)$, which has a one to one correspondence with modular invariants of free bosonic theory compactified on co-root lattice of a rank $l$ Lie group. Then a large number of modular invariants of affine Lie algebras are derived explicitly. As two applications of this method, we give a direct derivation of $D$-series of $SU(N)$ and a new proof for the A-D-E classification of the $SU(2)_k$ partition functions.