Re: Beginner--[Please Help]How to get coefficient list issued from a Series Command

*To*: mathgroup at smc.vnet.net*Subject*: [mg70201] Re: Beginner--[Please Help]How to get coefficient list issued from a Series Command*From*: dimmechan at yahoo.com*Date*: Sat, 7 Oct 2006 07:07:40 -0400 (EDT)*References*: <eg2e8k$73m$1@smc.vnet.net><eg4sik$fen$1@smc.vnet.net>

lst = (a[#1] + b[#1]*x + c[#1]*x^2 & ) /@ Range[3] {a[1] + x*b[1] + x^2*c[1], a[2] + x*b[2] + x^2*c[2], a[3] + x*b[3] + x^2*c[3]} selectCoeff[lis_List, x_] := Cases[lis, x[_], Infinity] (selectCoeff[lst, #1] & ) /@ {a, b, c} {{a[1], a[2], a[3]}, {b[1], b[2], b[3]}, {c[1], c[2], c[3]}} Apply[Plus, %, 1] {a[1] + a[2] + a[3], b[1] + b[2] + b[3], c[1] + c[2] + c[3]} dimmechan at yahoo.com wrote: > Hello. > > What you need is very easy. But in order to do programming I need to > modify a little your K list. > For example the first element of the list, a1+b1 x +c1 x^2 was > modified to a[1]+b[1]x+c[1]x^2 which > apart for issues of programming is the proper one since as said you > deal with power series. > > First define the list > > lst = (a[#1] + b[#1]*x + c[#1]*x^2 & ) /@ Range[3] > {a[1] + x*b[1] + x^2*c[1], a[2] + x*b[2] + x^2*c[2], a[3] + x*b[3] + > x^2*c[3]} > > Then use Cases > > Cases[lst, a[_], Infinity] > {a[1], a[2], a[3]} > Cases[lst, b[_], Infinity] > {b[1], b[2], b[3]} > Cases[lst, c[_], Infinity] > {c[1], c[2], c[3]} > > and here is the desired user-defined function > > selectCoeff[lis_List, x_] := Cases[lis, x[_], Infinity] > > (*check*) > > selectCoeff[lst, a] > {a[1], a[2], a[3]} > > If you insist on taking the result as {a1,a2,a3} (bad for you...) type > > % /. {a[1] -> a1, a[2] -> a2, a[3] -> a3} > {a1, a2, a3} > > Regards > Dimitris