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[223]:= $Version
Out[223]= 4.1 for Mac OS X (November 5, 2001)
In[225]:= a1 = DSolve[D[u[x, y], x, x] == 0, u[x,y], {x, y}]
Out[225]= {{u[x, y] -> C[1][y] + x C[2][y]}}
In[226]:= a2 = DSolve[D[u[x, y], y, y] == 0, u[x,y], {x, y}]
Out[226]= {{u[x, y] -> C[1][x] + y C[2][x]}}
The results are valid by inspection and, indeed,
In[229]:= D[u[x,y]/.a1[[1]],x,x]
Out[229]= 0
In[230]:= D[u[x,y]/.a2[[1]],y,y]
Out[230]= 0
Am I missing something? Perhaps your mail message does not accurately
reflect your actions. Did you read the help concerning the arbitrary
functions C[n]?
Tom Burton
On 3/17/02 2:52 AM, in article a71sgj$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[1][x]+C[2][y] .
>
> This result is ridiculous !!!!
> How it is possible?
>
>
>
> Diego