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MathGroup Archive 2007

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monomials in Graded Lexicographic Order and associated factorials

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73787] monomials in Graded Lexicographic Order and associated factorials
  • From: "er" <erwann.rogard at gmail.com>
  • Date: Wed, 28 Feb 2007 04:37:43 -0500 (EST)

hi,

i just want to share my code below and ask for any suggestion to speed
up the function FactorialList below,
which takes up about as much time to complete as PowerList, mostly due
to function aux. storing a table of values to avoid repeated
computation seems to be the easiest solution. however, i'm hoping to
avoid that, perhaps by exploiting the particular GLO structure.
thanks.

here's the usage i'm interested in: "PowerList[GDO,max,{x1,...,xD}]
returns { {{x1\^p1*...*xD^pD:|p|=q},q=0,...,max } where |p|=p1+...+pD;
FactorList[GDO,D,max] returns the corresponding mv-factorial terms:
{ {p1!*...*pD!:|p|=q},q=0,...,max }", e.g.

In[1] := PowerList[GLO, 2, {a, b, c}]
FactorialList[GLO, d, 2]
Out[2] = {{1}, {a, b, c}, {a ^ 2, a b, a c, b^ 2, b c, c^ 2}}
Out[2] = {{1}, {1, 1, 1}, {2, 1, 2, 1, 1, 2}}

code:
GLO/:PowerList[GLO,0,vars_]:={{1}};
GLO/:PowerList[GLO,p_,vars_]:=With[{rev=Reverse[vars]}, Join[{{1}},
Flatten/@Map[Reverse,           NestList[rev*Flatten/
@foldList[#]&,List/@rev,p-1],2]] ];
GLO/: FactorialList[GLO,d_,p_]:=Map[Times@@Factorial[#]&,aux[d,p],{2}];



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