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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: [mg54429] Re: How do I get a DSolve'd function
  • From: Curt Fischer <tentrillion at gmail.NOSPAM.com>
  • Date: Sun, 20 Feb 2005 00:09:48 -0500 (EST)
  • References: <cv6t29$6su$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Skirmantas 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?  

In[4]:=
sol=DSolve[{f'[x]\[Equal]-3f[x],f[0]\[Equal]10},f,x];sol//InputForm

Out[4]//InputForm=
{{f -> Function[{x}, 10/E^(3*x)]}}

In[2]:=
g[y_]:=f[x]/.sol[[1]]/.x -> y

In[5]:=
g[1]//InputForm

Out[5]//InputForm=
10/E^3

-- 
Curt Fischer


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