DSolve question
- To: mathgroup at smc.vnet.net
- Subject: [mg49129] DSolve question
- From: "James A. Smith" <jasmith at cim.mcgill.ca>
- Date: Fri, 2 Jul 2004 02:01:33 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
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.
As far as I can tell, I've only done a simple find-and-replace of the
variable names.
I looked up a related "dvnoarg" problem that appeared on the MathGroup
archive (http://forums.wolfram.com/mathgroup/archive/2003/Dec/msg00119.html)
and performed the same fine-and-replace:
Input 3: DSolve[y''[x] == ay'[x] + y[x], y[x], x]
Input 4: DSolve[x''[t] == ax'[t] + x[t], x[t], t]
Both of these seem to work out fine.
I'm using Mathematica 4.2 (OS X)...
Thank you,
James Smith