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MathGroup Archive 2005

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Re: How do I get a DSolve'd function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54457] Re: [mg54384] How do I get a DSolve'd function
  • From: DrBob <drbob at bigfoot.com>
  • Date: Sun, 20 Feb 2005 00:11:22 -0500 (EST)
  • References: <200502190733.CAA06184@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

sol = Last@DSolve[{f'[x] == -3f[x], f[0] == 10}, f[x], x]
Plot[f[x] /. sol, {x, 0, 10}]

or

sol = DSolve[{f'[x] == -3f[x], f[0] == 10}, f, x]
Plot[f[x] /. sol, {x, 0, 10}]

or

Clear@f
f = f /. Last@DSolve[{f'[x] == -3f[x], f[0] == 10}, f, x]
Plot[f@x, {x, 0, 10}]

or

sol = DSolve[{f'[x] == -3f[x], f[0] == 10}, f, x]
Plot[f@x /. First@sol, {x, 0, 10}]

The third method may be the one you like best.

Bobby

On Sat, 19 Feb 2005 02:33:01 -0500 (EST), Skirmantas <skirmantas.janusonis at yale.edu> wrote:

> I hope this is the last question for now.
>
> I can solve a differential equation and plot it by doing something
> like this:
>
> sol=DSolve[{f'[x]==-3f[x],f[0]==10},f,x]
> Plot[f/.sol,{x,0,10}]
>
> But how do I get the function f[x] itself? I want to be able to input
> f[x] and get its definition. Or do Plot[f[x],{x,0,10}]. Or define
> y[x_]:=f[x]^2.
>
> f[x]/.sol or f[x_]:=f[x]/.sol or f[x_]:=sol[[n,n,n]] do not work.
>
> What if the solution is a function with many variables, say u[x,y,z]?
> What's the correct way to "get" it?
>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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