Published online by Cambridge University Press: 15 April 2002
The complexity of computing, via threshold circuits, the iterated
product and powering of fixed-dimension $k\times k$ matrices
with integer or rational entries is studied. We call these two
problems $\sf IMP_k$
and $\sf MPOW_k$
, respectively, for short. We prove that:
(i) For $k\geq2$
, $\sf IMP_k$
does not belong to ${\rm TC}^0$
, unless
${\rm TC}^0={\rm NC}^1$
.newline
(ii) For stochastic matrices : $\sf IMP_2$
belongs to ${\rm TC}^0$
while, for $k\geq3$
, $\sf IMP_k$
does not belong to ${\rm TC}^0$
,
unless ${\rm TC}^0={\rm NC}^1$
.
(iii) For any k, $\sf MPOW_k$
belongs to ${\rm TC}^0$
.