Powder Diffraction

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The TOPAS symbolic computation system

A. A. Coelhoa1 c1, J. Evansa2, I. Evansa2, A. Kerna3 and S. Parsonsa4

a1 72 Cedar Street, Wynnum, 4178 Brisbane, Australia

a2 Department of Chemistry, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK

a3 Bruke rAXS, Karlsruhe, Germany

a4 School of Chemistry, The University of Edinburgh, King’s Buildings, W. Mains Road, Edinburgh, Scotland, EH9 3JJ


Computer algebra removes much of the drudgery from mathematics; it allows users to formulate models by using the language of mathematics and to have those models evaluated with little effort. This symbolic form of representation is often thought of as being separate to dedicated computational programs such as Rietveld refinement. These dedicated programs are often written in low level languages; they are relatively inflexible in what they do and modifying them to change functionality in a small manner is often a major programming task. This paper describes a symbolic system that is integrated into the dedicated Rietveld refinement program called TOPAS. The symbolic component allows large functional changes to be made at run time and with a relatively small amount of effort. In addition, the system as a whole reduces the programming complexity at the developmental stage.

(Received October 20 2011)

(Accepted October 22 2011)

Key words

  • symbolic computation;
  • computer algebra;
  • Rietveld refinement


c1 Author to whom correspondence should be addressed. Electronic mail: AlanCoelho@bigpond.com