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Re: Forcing mathematica to output a certain form

  • To: mathgroup at smc.vnet.net
  • Subject: [mg108140] Re: Forcing mathematica to output a certain form
  • From: Geico Caveman <spammers-go-here at spam.invalid>
  • Date: Tue, 9 Mar 2010 06:21:57 -0500 (EST)
  • References: <hn2mkv$4bc$1@smc.vnet.net>

On 2010-03-08 04:22:07 -0700, Bob Hanlon <hanlonr at cox.net> said:

>
> expr = f[t] + g[t] y'[t] == h[t] y[t]^2;
>
> Reverse[Expand[
>    Equal @@
>     Solve[expr /.
>        f[t] -> -z*g[t], z][[1, 1]]] /.
>
>    z -> -f[t]/g[t]]
>
> Derivative[1][y][t] - (h[t]*y[t]^2)/g[t] == -(f[t]/g[t])
>
> Expand[
>   (First[expr] - Last[expr])/g[t]] == 0
>
> f[t]/g[t] - (h[t]*y[t]^2)/g[t] + Derivative[1][y][t] == 0
>
>
> Bob Hanlon
>
> ---- Geico Caveman <spammers-go-here at spam.invalid> wrote:
>
> =============
> As a result of an Eliminate function, and subsequent (wrapper)
> simplification under some conditions, I am getting a non-linear
> differential equation.
>
> It looks like:
>
> f(t)+g(t) y'(t)=h(t) y^2(t)
>
> Is there a way to force mathematica to output this in the way a
> differential equation is best written:
>
> y'(t)+h(t)/g(t) y^(t) = -f(t)/g(t)
>
> or
>
> the transposed form with zero on RHS ?

Thanks for your response (and the other person's response).

So, I take it that there is no way to tell Mathematica to output it in
a standard form for differential equations, short of "doing it by hand"
?


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