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Communications of the ACM

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ACM President's Letter: ACM government

A new technique for compression and storage of data

The widespread tendency toward storage of large programs and blocks of text has produced a need for efficient methods of compressing and storing data. This paper describes techniques that can, in most cases, decrease storage  …

A user authentication scheme not requiring secrecy in the computer

In many computer operating systems a user authenticates himself by entering a secret password known solely to himself and the system. The system compares this password with one recorded in a Password Table which is availableAll …

A high security log-in procedure

The protection of time sharing systems from unauthorized users is often achieved by the use of passwords. By using one-way ciphers to code the passwords, the risks involved with storing the passwords in the computer can be avoided …

Execution time requirements for encipherment programs

Although encipherment has often been discussed as a means to protect computer data, its costs are not well established. Five experiments were conducted to measure the cpu time on a CDC 6400 required by additive ciphers programmed …

Graph coloring conditions for the existence of solutions to the timetable problem

A necessary and sufficient condition is presented for the existence of a solution to the Gotlieb class-teacher timetable problem. Several relationships are established between the class-teacher timetable problem and graphs with …

A new solution of Dijkstra's concurrent programming problem

A simple solution to the mutual exclusion problem is presented which allows the system to continue to operate despite the failure of any individual component.

On the conversion of programs to decision tables: method and objectives

The problems of converting programs to decision tables are investigated. Objectives of these conversions are mainly program debugging and optimization in practice. Extensions to the theory of computation and computability are …

Procedures for computing smoothing and interpolating natural splines

Algorithm 481: Arrow to precedence network transformation

Algorithm 482: Transitivity sets

Remark on algorithm 454 [E4]: The complex method for constrained optimization

Remark on algorithm 450[E4]:Rosenbrock function minimization

Gauss harmonic interpolation formulas

Let R be an open, bounded, simply connected region in the (x,y)-plane and let (x*,y*) be a point in R. Assuming R is starlike with respect to (x*,y*), we discuss a method for computing Gauss harmonic interpolation formulas for …

Interpolation with rounded ramp functions

A new interpolation function is introduced. It has infinitely many continuous derivatives and is a composition of ramp functions with smoothed bends called Rounded Ramp Functions. How the interpolation function can be extended …

Recurrence relations for the Fresnel integral 0
exp -ctdtt 1+t2

The class of functions defined by ∫0[exp(-cX)dt/(1 + Y) (√t)k] where X and Y are either t or t2 and k is -1, 0, or 1 can be evaluated by recurrences for all but small values of the parameter c. These recurrences, given here, …

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