Andrew D. Booth

A New Fourier Refinement Technique

IT has been shown by Cochran1 that the ordinary process of Fourier refinement, used in X-ray structure analysis, is equivalent to minimizing the function: where f is f (h,k,l), the mean atomic scattering factor for the (h,k,l) plane; F0 is F0 (h,k,l), the observed structure factor ; and Fc is Fc(h,k,l), the calculated structure factor.

The efficiency of certain methods of information retrieval

Methods are discussed for the retrieval of items of data which are stored as entries in a table in the store of a computer. The average number of look-up operations required to find an entry is computed for several methods. It is shown that if advantage is taken of the relative frequencies with which the different entries are looked up, the average number of look-ups may be substantially reduced. The results are applied to the problem of using a computer as a mechanical dictionary.

Machines of the Past

The Computer from Pascal to von Neumann.By Herman H. Goldstine. Pp. x + 378. (University of Princeton: Princeton, New Jersey, January 1973.) £6.25.