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MathGroup Archive 2003

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Re: polynomial operations through CoefficientList

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44766] Re: polynomial operations through CoefficientList
  • From: "Peltio" <peltio at twilight.zone>
  • Date: Tue, 25 Nov 2003 00:45:35 -0500 (EST)
  • References: <bps3jo$9pu$1@smc.vnet.net>
  • Reply-to: "Peltio" <peltioNOSP at Miname.com.invalid>
  • Sender: owner-wri-mathgroup at wolfram.com

"Paolo Bientinesi" wrote

>Given cf1 = {1,k1,-2 k2} and cf2 = {-2,-k3}
>
>I would like to get the list
>{-2,-2 k1-k3,4 k2-k1 k3,2 k2 k3}
>for p1[x]*p2[x]

productList[cf1_,cf2_]:=ListConvolve[cf1, cf2, {1, -1}, 0]

>and the list
>{-1,k1-k3,-2 k2}
>for p1[x]+p2[x]

You need some padding here.
If you can supply the missing coeffients in your input, such as in

cf1 = {1,k1,-2 k2};
cf2 = {-2,-k3,0}

You just have to sum the two lists

sumList[cf1_,cf2_]:= cf1+cf2

otherwise you'll have to add a couple of lines to pad the shortest list with
zeros up the the lenght of the longest one. Something like this would do:

sumList[cf1_,cf2_]:=Module[
    {n=Max[Length[cf1],Length[cf2]]},
    PadRight[cf1,n]+PadRight[cf2,n]
]

I haven't had a chanche to test the procedures, though. Check'em out prior
to using them.

cheers,
Peltio
invalid address in reply-to. Crafty demunging required to mail me.




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