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Contents - Student subdomain for University of Bath

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Appendix C<br />

Systems<br />

This appendix discusses various computer algebra systems, especially from the<br />

point <strong>of</strong> view <strong>of</strong> their internal data structures and algorithms, and how this<br />

relates to the ideas expressed in the body <strong>of</strong> this book. We do not discuss the<br />

user interfaces as such, nor is this intended to replace any manuals, or specialist<br />

books.<br />

Moses [Mos71] described systems as falling into various categories, depending<br />

on the extent <strong>of</strong> automatic trans<strong>for</strong>mation. While most systems today are what<br />

Moses would call ‘new left’, the extent <strong>of</strong> automatic trans<strong>for</strong>mation still varies<br />

dramatically.<br />

C.1 Axiom<br />

C.1.1<br />

Overview<br />

See Figure C.1.<br />

We note that the polynomials have been expanded and the greatest common<br />

divisor cancelled (in the terminology <strong>of</strong> Definition 4 we have canonical <strong>for</strong>ms <strong>for</strong><br />

this data type). We are told the data type <strong>of</strong> the result, Fraction Polynomial<br />

Integer, i.e. the field <strong>of</strong> fractions <strong>of</strong> Z[variables]. In fact, this answer happens<br />

to have denominator 1, so lies in Polynomial Integer, but the system does<br />

not automatically check <strong>for</strong> such retractions.<br />

C.1.2<br />

History<br />

This system [JS92], with which the author has been heavily involved, can be<br />

seen as the first <strong>of</strong> the ‘Bourbakist’ 1 systems — since followed, in particular,<br />

by Magma [BCM94] and SAGE. It was developed at IBM Yorktown Heights,<br />

1 Nicolas Bourbaki was the pseudonym <strong>of</strong> a group <strong>of</strong> mathematicians, largely French,<br />

who wrote very influential abstract mathematical texts from the 1930s on. See http:<br />

//www-history.mcs.st-andrews.ac.uk/HistTopics/Bourbaki_1.html.<br />

231

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