Re: Recombining CoefficientList
- Subject: [mg2504] Re: Recombining CoefficientList
- From: mtrott (Michael Trott)
- Date: Wed, 15 Nov 1995 06:59:45 GMT
- Approved: usenet@wri.com
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: Wolfram Research, Inc.
- Sender: daemon at wri.com ( )
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.