Re: Recombining CoefficientList
- To: mathgroup at smc.vnet.net
- Subject: [mg2504] Re: Recombining CoefficientList
- From: mtrott (Michael Trott)
- Date: Wed, 15 Nov 1995 01:59:45 -0500
- Organization: Wolfram Research, Inc.
In article <489hte$gm7 at ralph.vnet.net> sherod at boussinesq.Colorado.EDU
(Scott Herod) writes:
> CoefficientList[poly, {x1,x2,...,xn}] returns an array of coefficients
> of the various powers of the xi in poly. Has someone got a code segment
> to recreate poly from the list of xi and the output?
FromCoefficientListToPolynom[coeffList_List, varList_List] :=
Plus @@ Flatten[MapIndexed[(#1 Inner[Power, varList,
#2 - 1, Times])&, coeffList, {Length[varList]}]]
example:
In[6]:= CoefficientList[(x^3 + 7x - y)^3, {x, y, z}]
Out[6]= {{{}, {}, {}, {-1}}, {{}, {}, {21}, {}}, {{}, {-147}, {}, {}},
> {{343}, {}, {3}, {}}, {{}, {-42}, {}, {}}, {{147}, {}, {}, {}},
> {{}, {-3}, {}, {}}, {{21}, {}, {}, {}}, {}, {{1}, {}, {}, {}}}
In[7]:= FromCoefficientListToPolynom[%, {x, y, z}]
3 5 7 9 2 4 6
Out[7]= 343 x + 147 x + 21 x + x - 147 x y - 42 x y - 3 x y +
2 3 2 3
> 21 x y + 3 x y - y
In[8]:= Factor[%]
3 3
Out[8]= (7 x + x - y)
--
Michael Trott
Wolfram Research, Inc.