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MathGroup Archive 2004

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Re: Re: DSolve question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49164] Re: [mg49155] Re: DSolve question
  • From: James Smith <jasmith at cim.mcgill.ca>
  • Date: Tue, 6 Jul 2004 03:33:23 -0400 (EDT)
  • References: <200407050854.EAA14799@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Starting a fresh session was the key to solving this problem.

thanks to everyone who pointed it out. :-)

-James

On 5-Jul-04, at 4:54 AM, Bill Rowe wrote:

> 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.
> --
> To reply via email subtract one hundred and four
>
>
James Andrew Smith
PhD Candidate, Mechanical Engineering
Ambulatory Robotics Lab
McGill University
Web: www.cim.mcgill.ca/~jasmith
Phone: 514-398-8054


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