2005 | OriginalPaper | Buchkapitel
Sequences of Radius k: How to Fetch Many Huge Objects into Small Memory for Pairwise Computations
verfasst von : Jerzy W. Jaromczyk, Zbigniew Lonc
Erschienen in: Algorithms and Computation
Verlag: Springer Berlin Heidelberg
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Let
a
1
,
a
2
, ...,
a
m
be a sequence over [n]={1,...
n
} We say that a sequence
a
1
,
a
2
, ...
a
m
has the
k-radius
property if every pair of different elements in [n] occurs at least once within distance at most
k
; the
distance
d
(
a
i
,
a
j
) = |
i
−
j
|. We demonstrate lower and (asymptotically) matching upper bounds for sequences with the
k-radius
property. Such sequences are applicable, for example, in computations of two-argument functions for all
$\binom{n}{2}$
pairs of large objects such as medical images, bitmaps or matrices, when processing occurs in a memory of size capable of storing
k
+ 1 objects,
k
<
n
. We focus on the model when elements are read into the memory in a FIFO fashion that correspond to streaming the data or a special type of caching. We present asymptotically optimal constructions; they are based on the Euler totient theorem and recursion.