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Re: ODE in mathematica. what is wrong?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91317] Re: ODE in mathematica. what is wrong?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 15 Aug 2008 06:53:39 -0400 (EDT)
  • References: <g813bb$4r$1@smc.vnet.net>

Hi,

the first thing whats wrong is, that
you have 3 equations for y[x] and the solution
of

y'[x] == -\[Rho]y[x]

is different form the solution

  I\[HBar] y'[x] == \[Epsilon]y[x]

and has nothing to do with the solution of

y''[x] + 2 \[Rho]y'[x] + k^2 == 0

The second thing that is wrong, is that you call
NDSolve[] instead of DSolve[] and the third thing
is that you use Subscript[y,0] as initial value,
because you have said  that the symbol "y" stand
for the solution function in the
ode and it can't be the solution *and* the inital value.

But

DSolve[#, y[x], x] & /@
  {{y'[x] == -\[Rho] y[x],
    y[0] == Subscript[\[ScriptY],
      0]}, {I \[HBar] y'[x] == \[Epsilon] y[x],
    y[0] == Subscript[\[ScriptY], 0]}, {y''[x] + 2 \[Rho] y'[x] +
      k^2 == 0, y'[0] == Subscript[g, 0]}}

work as it should.

Regards
   Jens




hoi-su jung wrote:
> Hi,
> I am a freshman of Mathematica, I need help here...
> 
> I met such problem as:
> 
> NDSolve[{ y'[x] == -\[Rho]y[x], y[0] == Subscript[y, 0], 
>   I\[HBar] y'[x] == \[Epsilon]y[x], y[0] == Subscript[y, 0], 
>   y''[x] + 2 \[Rho]y'[x] + k^2 == 0, y'[0] == Subscript[g, 0]}, y, x]
> NDSolve::dvnoarg: The function y appears with no arguments.
> 
> How to Handle???
> 


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