Re: S.O.S. , please......
- To: mathgroup at smc.vnet.net
- Subject: [mg25932] Re: S.O.S. , please......
- From: "Bill Bertram" <wkb at ansto.gov.au>
- Date: Thu, 9 Nov 2000 03:04:28 -0500 (EST)
- Organization: Australian Nuclear Science and Technology Organisation
- References: <8ual38$auc@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
alessandro agresti <agresti at dffs.unifi.it> wrote in message news:8ual38$auc at smc.vnet.net... > I have the following function: > > y(R) = A * [R^b] * [exp(-cR)] > > I know y0=y(r_0), y1=y ' (r_0), y2=y " (r_0), where r_0 is know value. > > Can anybody tell me if: > > 1) mathematica can help me to find the analitic formulas for the > parameters : A, b, c > 2) if yes , please tell me which are the commands to give Mathematica. > 3) perhaps the better thing for me it is to receive the analitic formulas by > e-mail; Hi, Use the first equation to get A in terms of b and c. A = y0*Exp[c r0]/r0^b. then Mathematica can solve the remaining two equations eg, y[r_] := A r^b Exp[-c r] Solve[ReplaceAll [{D[y[r0],r0] == y1, D[y[r0], {r0,2}] == y2}, A -> y0 Exp[c r0]/r0^b], {b,c}] This will give you the analytic solutions for b and c from which you can then get A. Cheers, Bill