Simultaneous WRITES of parallel random access machines do not help to compute simple arithmetic functions

Journal Article · Thu Jan 01 04:00:00 EST 1987 · J. Assoc. Comput. Mach.; (United States)

DOI:https://doi.org/10.1145/7531.22944· OSTI ID:6576319

Reischuk, R

The ability of the strongest parallel random access machine model WRAM is investigated. In this model different processors may simultaneously try to write into the same cell of the common memory. It has been shown that a parallel RAM without this option (PRAM), even with arbitrarily many processors, can almost never achieve sublogarithmic time. On the contrary, every function with a small domain like binary values in case of Boolean functions can be computed by a WRAM in constant time. The machine makes fast table look-ups using its simultaneous write ability. The main result of this paper implies that in general this is the ''only way'' to perform such fast computations and that a domain of small size is necessary. Otherwise simultaneous writes do not give an advantage. Functions with large domains for which any change of one of the n arguments also changes the result are considered, and a logarithmic lower time bound for WRAMs is proved. This bound can be achieved by machines that do not perform simultaneous writes. A simple example of such a function is the sum of n natural numbers.

• Research Organization: Universitat Bielefeld
• OSTI ID: 6576319
• Journal Information: J. Assoc. Comput. Mach.; (United States), Journal Name: J. Assoc. Comput. Mach.; (United States) Vol. 34:1; ISSN JACOA
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
990210* -- Supercomputers-- (1987-1989)
ALGORITHMS
COMPUTER CODES
COMPUTERIZED SIMULATION
FUNCTIONS
MATHEMATICAL LOGIC
MATHEMATICS
MEMORY DEVICES
PARALLEL PROCESSING
PROGRAMMING
RANDOMNESS
SIMULATION
TIME DEPENDENCE
W CODES