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