       Re: ridiculous results with DSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg33370] Re: ridiculous results with DSolve
• From: Thomas Burton <tburton at brahea.com>
• Date: Mon, 18 Mar 2002 00:18:47 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Hello Diego,

In:= \$Version
Out= 4.1 for Mac OS X (November 5, 2001)

In:= a1 = DSolve[D[u[x, y], x, x] == 0, u[x,y], {x, y}]
Out= {{u[x, y] -> C[y] + x C[y]}}

In:= a2 = DSolve[D[u[x, y], y, y] == 0, u[x,y], {x, y}]
Out= {{u[x, y] -> C[x] + y C[x]}}

The results are valid by inspection and, indeed,

In:= D[u[x,y]/.a1[],x,x]
Out= 0

In:= D[u[x,y]/.a2[],y,y]
Out= 0

Am I missing something? Perhaps your mail message does not accurately
functions C[n]?

Tom Burton

On 3/17/02 2:52 AM, in article a71sgj\$gh9\$1 at smc.vnet.net, "Diego Catalano
Ferraioli" <diego_catalano_ferraioli at yahoo.com> wrote:

> 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[x]+C[y] .
>
> This result is ridiculous !!!!
> How it is possible?
>
>
>
>                 Diego

```

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