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Re: S.O.S. , please......

  • To: mathgroup at
  • Subject: [mg25932] Re: S.O.S. , please......
  • From: "Bill Bertram" <wkb at>
  • Date: Thu, 9 Nov 2000 03:04:28 -0500 (EST)
  • Organization: Australian Nuclear Science and Technology Organisation
  • References: <8ual38$>
  • Sender: owner-wri-mathgroup at

alessandro agresti <agresti at> wrote in message
news:8ual38$auc at
> 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
> 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
> e-mail;


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.



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