Re: Forcing mathematica to output a certain form
- To: mathgroup at smc.vnet.net
- Subject: [mg108235] Re: Forcing mathematica to output a certain form
- From: magma <maderri2 at gmail.com>
- Date: Thu, 11 Mar 2010 06:37:01 -0500 (EST)
- References: <hn2mkv$4bc$1@smc.vnet.net> <hn5c96$7ng$1@smc.vnet.net>
On Mar 9, 12:43 pm, Geico Caveman <spammers-go-h... at spam.invalid> wrote: > On 2010-03-08 04:22:07 -0700, Bob Hanlon <hanl... 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-h... 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" > ? No, you come to the wrong conclusion. The task you require is not too difficult to program. You can create a function which takes an equation (== sign) and rearranges everything as you wish. You need to learn programming Mathematica a bit. It is well worth. I have no time to do it for you right now. Perhaps some other member. Try yourself. It is a very rewarding experience.