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MathGroup Archive 2001

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Re: 2nd order differential equation help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31521] Re: 2nd order differential equation help
  • From: "Angel E. Andreu" <aandreu at localnet.com>
  • Date: Thu, 8 Nov 2001 04:57:31 -0500 (EST)
  • References: <9sb4rb$h1n$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Peter try:

eqn1[t_] := g'[t] + 0.1g[t] + g[t]  //this is what you had: eqn1[t_] =
g'[t] + 0.1g[t] + ?g[t] == 0

eqn[t_] := g''[t] + 0.1g'[t] + g[t]

solution =
  DSolve[{eqn[t] == eqn1[t], g'[0] == 1, g[0] == 0}, g[t], t, {t, 0, 10
Pi}]

Which produces the following output

{{g[t] -> Exp[-0.1t] (-0.909091 + 0.909091Exp[1.1t) }}

A²

Peter Dimitriou wrote:

> Exactly how do I get this into a form Mathamatica will accept?  It has
> been a number of years since enrolling in diffeq, however I think I am
> close to correct but would appreciate help.
>
> the problem;
>
> Solve the differential equation:
>
> g''(t) + 0.1 g'(t) + g(t) = 0
>
> where the previous equation uses conventional mathematical notation.
> You must transfrom the equation and initial conditions into
> Mathematica syntax.
>
> for t between 0 and 10 Pi
>
> subject to the initial conditions
>         g(0) = 0,
>         g'(0) = 1
>
> Plot your results.
>
> My attempt is as follows:
>
> Clear[g]
>
> Clear[eqn]
>
> eqn[t_] = g''[t] + 0.1g'[t] + g[t] == 0
>
> Clear[eqn1]
>
> eqn1[t_] = g'[t] + 0.1g[t] + ?g[t] == 0
>
> solution = DSolve[{eqn[t], eqn1[t]}, g'[0] == 1,
> g[0] == 0, g[t], {t, 0, 10\[Pi]}]
>
> DSolve::dsvar: g[0]==0 cannot be used as a variable.
>
> what am I dont doing right?  any suggestions helpful

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