Re: ridiculous results with DSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg33371] Re: [mg33363] ridiculous results with DSolve
• From: BobHanlon at aol.com
• Date: Mon, 18 Mar 2002 00:18:48 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```In a message dated 3/17/02 7:39:09 AM, diego_catalano_ferraioli at yahoo.com
writes:

>Actually I'm interested in implementation of algoritms based on the Lie
>
>theory of differential equations.
>I was searching for a suitable language for an efficient implementation
>
>of these algoritms when I discovered that (for example):
> if you try to solve with Mathematica the trivial PDE
>
>
>D[u[x,y],x,x]==0
>
>   then a Dump occurs, but if you try to solve the equivalent equation
>
>
>D[u[x,y],y,y]==0
>
>  then Mathematica gives the wrong solution
>
>                                                      u[x,y]=
>C[1][x]+C[2][y] .
>
>This result is ridiculous !!!!
>How it is possible?
>

Works fine on my system

\$Version

4.1 for Mac OS X (November 5, 2001)

DSolve[D[u[x,y],x,x]==0, u[x,y], {x,y}]

{{u[x, y] -> C[1][y] + x*C[2][y]}}

DSolve[D[u[x,y],{x,2}]==0, u[x,y], {x,y}]

{{u[x, y] -> C[1][y] + x*C[2][y]}}

DSolve[D[u[x,y],y,y]==0, u[x,y], {x,y}]

{{u[x, y] -> C[1][x] + y*C[2][x]}}

DSolve[D[u[x,y],{y,2}]==0, u[x,y], {x,y}]

{{u[x, y] -> C[1][x] + y*C[2][x]}}

Bob Hanlon
Chantilly, VA  USA

```

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