[Axiom-developer] [Axiom-mail] Lexicographic order

[Jens Axel Søgaard]

Changes http://page.axiom-developer.org/zope/mathaction/AxiomMail/diff
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Hi all,

Is there a smarter way than the following to write lexorder?(p,q) ?

lexorder?(p,q) ==
   if empty?(variables(p))
   then return ~empty(variables(q))
   else
     vars := members(difference( set(variables( secret1*p + secret2*q)),
                                 set([secret1, secret2])))
     a := members(degree( p::DMP(vars,?) ))
     b := members(degree( q::DMP(vars,?) ))
     return negative?( first(a) - first(b) )


My first attempt used:

   vars := sort(members(union(set(variables(p), variables(q)))))

but was surprised to see

  > sort([x,y,z])
  [z,y,x]

  > sort([x,z,y])
  [y,z,x]

and thus made up the secret-trick in order to avoid sort.

-- 
Jens Axel S�gaard



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