Re: minimal power

*To*: mathgroup at smc.vnet.net*Subject*: [mg50255] Re: minimal power*From*: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>*Date*: Mon, 23 Aug 2004 06:34:21 -0400 (EDT)*References*: <cg96v1$a3l$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Firstly, it is not a good idea to use D as a variable name because it is reserved for doing differentiation. The safe bet is to use variable names that start with a lowercase character. Define your series (you can use e rather than f with no problems) s = a/t^(5/2) + b/t^(3/2) + c/t^2^(-1) + d*t^(1/2) + e*t^(3/2); If this were a polynomial then CoefficientList[s, t] would extract the various powers, but here you have to be cleverer. There are lots of ways to do what you want, but one that will be generally useful here and elsewhere is to evaluate FullForm[s], which gives Plus[Times[a, Power[t, Rational[-5, 2]]], Times[b, Power[t, Rational[-3, 2]]], Times[c, Power[t, Rational[-1, 2]]], Times[d, Power[t, Rational[1, 2]]], Times[e, Power[t, Rational[3, 2]]]] This tells you that the various powers of t are represented as Power[t, Rational[x_, y_]], where x_ and y_ are patterns that match to any arguments of Rational. Now use this to extract the various powers of t in s (extracting only the powers and omitting the base t): p = Cases[s, Rational[x_, y_], 3]; This gives p as the list {-(5/2), -(3/2), -(1/2), 1/2, 3/2}. {Min[p],Max[p]} then gives you the minimum and maximum powers of t. This approach can be generalised. You start by looking at FullForm[expression] and then design an appropriate Cases expression that pulls out the pieces that you want. Steve Luttrell "Nodar Shubitidze" <shubi at nusun.jinr.ru> wrote in message news:cg96v1$a3l$1 at smc.vnet.net... > Hi ! > > I have for example following expression: > S = A t^(-5/2) + B t^(-3/2) + C t^(-1/2) + D t^(1/2) + F t^(3/2); > Eith command "Exponent[S,t]" I can receive maximal power of S. > Why I may calculate minimal power of S ? > With best regards > Nodar Shubitidze > Joint Institute for Nuclear Research > Dubna, RUSSIA >