Matrix Code

Matrix Code gives imperative programming a mathematical semantics and heuristic power comparable in quality to functional and logic programming. A program in Matrix Code is developed incrementally from a specification in pre/post-condition form. The computations of a code matrix are characterized by powers of the matrix when it is interpreted as a transformation in a space of vectors of logical conditions. Correctness of a code matrix is expressed in terms of a fixpoint of the transformation. The abstract machine for Matrix Code is the dual-state machine, which we present as a variant of the classical finite-state machine.Comment: 39 pages, 19 figures; extensions and minor correction

CROSS SECTIONS FOR SCATTERING OF ELECTRONS ON BF3

We calculate cross sections for elastic scattering and electronic excitation of BF3 molecules by low energy electrons. The R-Matrix code Quantemol-N has been used for calculations. The cross sections indicate the presence of a shape resonance of symmetry B-1 (A(2)'' in D-3h) at around 4.5 eV

R-matrix calculations of low-energy electron alkane collisions

Ab initio electron scattering calculations are presented for methane, ethane and propane with particular emphasis on elastic cross sections. Calculations are performed with the Quantemol-N expert system which runs the UK polyatomic R-matrix code. These calculations are presented which systematically increase the size of the coupled states expansion which is used to represent polarisation effects in the scattering wave function. Agreement with experimental measurements is obtained provided sufficient coupled states are included in the expansion. Whether these coupled states expansions really converge the polarisation potential and the prospects for further calculations are discussed. (c) 2007 Elsevier B.V. All rights reserved

Compiling Imperfectly-nested Sparse Matrix Codes with Dependences

We present compiler technology for generating sparse matrix code from (i) dense matrix code and (ii) a description of the indexing structure of the sparse matrices. This technology embeds statement instances into a Cartesian product of statement iteration and data spaces, and produces efficient sparse code by identifying common enumerations for multiple references to sparse matrices. This approach works for imperfectly-nested codes with dependences, and produces sparse code competitive with hand-written library code