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MathGroup Archive 2004

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Re: DSolve question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49155] Re: DSolve question
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Mon, 5 Jul 2004 04:54:45 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 7/2/04 at 2:01 AM, jasmith at cim.mcgill.ca (James A. Smith) wrote:

>Being a Mathematica novice, I'm confused by an error generated when
>I modify the following differential equation example:

>Input 1: DSolve[y'[x] == 2 a x, y[x], x] Output 1: {{y[x] -> a x^2
>+ C[1]}}

>This is fine.  But why does the following produce an error, since
>all I am doing is replacing the independent "x" variable with "t"
>and the dependent "y" variable with "x":

>Input 2: DSolve[x'[t] == 2 a t, x[t], t] (error) DSolve::dvnoarg:
>The function x appears with no arguments.

DSolve[Derivative[1][y][x] == 2*a*x, y[x], x]
{{y[x] -> a*x^2 + C[1]}}

DSolve[Derivative[1][x][t] == 2*a*t, x[t], t]
{{x[t] -> a*t^2 + C[1]}}

$Version
"4.2 for Mac OS X (August 22, 2002)"

As you can see, it seems to work fine for me. 

Here, all I did was copy and paste from your post to Mathematica in a fresh session. 
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