The TI -80 doesn't provide a direct way to work with them.That someone
can do to add matrices it's to work with them like a list

Example:
           1 2       5 6    6 8
                 +        =
           3 4       7 8    10 12

in the TI-80 one should do:
      {1,2,3,4}->L1 (enter); {5,6,7,8}->L2 (enter); L1+L2 (enter)

But, what to do in a multiplication of matrices?.

I made a little program that make  multiplication's of square matrices in
the TI-80; i'll hope that can help to someone.
                                                Ricardo Castro

1.- First, in STAT-EDIT, enter the "matrices"
2.- Then, run the next program:

PROGRAM:MATRIX
:CLRHOME
:DIM L1-> N
:0->DIM L3
:1->V
:FOR (I,1,N,(SQRT N))  /* SQRT = SQUARE ROOT)
:FOR (J,1,(SQRT N),1)
:SUM SEQ (( L1(I+L)L2(J+L(SQRT N)),L,0,(SQRT N)-1,1)->L3(V)
:V+1->V
:END
:END
:FOR(F,1,N,1)
:DISP L3(F)
:END
:STOP
:PRGM_MATRIX
: