Design and Implementation of a Homomorphic ... - Researcher
Design and Implementation of a Homomorphic ... - Researcher
Design and Implementation of a Homomorphic ... - Researcher
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So now consider the inner sum in (7). The weights w(e 1 ), . . . , w(e k ) are integers bounded by r<br />
in absolute value, <strong>and</strong> r is strictly less than m by the assumption 2r 2 ≤ H ≤ m. If any weight,<br />
say<br />
∑<br />
w(e 1 ), is non-zero, then τ w(e1) has multiplicative order dividing m, but not 1, <strong>and</strong> so the sum<br />
j τ jw(e1) vanishes, <strong>and</strong> hence<br />
∑<br />
( ∑<br />
)( ∑<br />
)<br />
τ j 1w(e 1 )+···+j k w(e k ) = τ j 1w(e 1 )<br />
τ j 2w(e 2 )+···+j k w(e k )<br />
= 0.<br />
j 1 ,...,j k j 1 j 2 ,...,j k<br />
Otherwise, if all the weights are w(e 1 ), . . . , w(e k ) are zero, then<br />
We therefore have<br />
∑<br />
P ={e 1 ,...,e k }<br />
(H/m) k<br />
∑<br />
j 1 ,...,j k<br />
τ j 1w(e 1 )+···+j k w(e k ) = m k .<br />
∑<br />
j 1 ,...,j k<br />
τ j 1w(e 1 )+···+j k w(e k ) =<br />
∑<br />
P ={e 1 ,...,e k }<br />
w(e 1 )=···=w(e k )=0<br />
H k , (8)<br />
Observe that any partition P = {e 1 , . . . , e k } with w(e 1 ) = · · · = w(e k ) = 0 can be formed by<br />
merging the edges <strong>of</strong> some perfect matching on the complete bipartite graph with vertex sets<br />
{1, . . . , r} <strong>and</strong> {r + 1, . . . , 2r}. The total number <strong>of</strong> such matchings is r! (see (2)). So we have<br />
r!H r ≤<br />
∑<br />
P ={e 1 ,...,e k }<br />
w(e 1 )=···=w(e k )=0<br />
∑r−1<br />
{ r<br />
H k ≤ r!H r + r! H<br />
k}<br />
k<br />
k=1<br />
k=1<br />
∑r−1<br />
{ r<br />
≤ 2r! H<br />
k}<br />
k (by Lemma 2)<br />
= 2r!(H r − H r ) (by (1))<br />
≤ 2r!r 2 H r−1 (by Lemma 1)<br />
Combining this with (7) <strong>and</strong> (8) proves the theorem.<br />
40