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Schlagwörter:
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Zusammenfassung:
We present a multi--party protocol for computing certain functions of
an $n\times k$ $0-1$ matrix $A$. The protocol is for $k$ players, where
player $i$ knows every column of $A$, except column $i$. {\it Babai,
Nisan}
and {\it Szegedy} proved that to compute $GIP(A)$ needs $\Omega (n/4^k)$
bits to communicate. We show that players can count those rows of matrix $A$
which sum is divisible by $m$, with communicating only $O(mk\log n)$ bits,
while counting the rows with sum congruent to 1 $\pmod m$ needs
$\Omega (n/4^k)$ bits of communication (with an odd $m$ and $k\equiv m\pmod
{2m}$). $\Omega(n/4^k)$ communication is needed also to count the rows
of $A$ with sum in any congruence class
modulo an {\it even} $m$.
The exponential gap in communication complexities allows us to prove
exponential lower bounds for the sizes of some bounded--depth circuits with
MAJORITY, SYMMETRIC and MOD$_m$ gates, where $m$ is an odd
-- prime or composite -- number.
