T Duality in M(atrix) Theory and S Duality in Field Theory
  The matrix model formulation of M theory can be generalized to compact transverse backgrounds such as tori. If the number of compact directions is K then the matrix model must be generalized to K+1 dimensional super Yang Mills theory on a compact space. If K is greater than or equal to 3, there are T dualities which which require highly nontrivial identifications between different SYM theories. In the simplest case we will see that the requirement reduces to the well known electric- magnetic duality of N=4 SYM theory in 3+1 dimensions. 
Leonard Susskind