Re: Solve[] handles the same system differently
- To: mathgroup at smc.vnet.net
- Subject: [mg40873] Re: Solve[] handles the same system differently
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Tue, 22 Apr 2003 06:49:35 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <b80k0i$m3f$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
if you introduce the new equation (and a new variable)
Mathematica get two equations for the same variable and
it can not resolve it. Try
Solve[{Rx == 3300, VinX1 == 0, VgsX1 == Rx*IdsX1,
IdsX1 == 0.001(1 - (VinX1 - VgsX1)/(-1.5))^2}, {IdsX1, VgsX1}]
Regards
Jens
Joe Gwinn wrote:
>
> I am running Mathematica 4.0.1.0 under MacOS 9.1, and have encountered a
> little mystery:
>
> The following works OK:
>
> In[15]:=
> Solve[{Rx == 3300, VinX1 == 0,
> IdsX1 == 0.001(1 - (VinX1 - Rx*IdsX1)/(-1.5))^2}, {IdsX1}]
>
> Yielding:
>
> Out[15]=
> {{IdsX1 -> 0.000234453}, {IdsX1 -> 0.00088125}}
>
> When I rearrange the equation system a bit, it fails to find a solution:
>
> In[16]:=
> Solve[{Rx == 3300, VinX1 == 0, VgsX1 == Rx*IdsX1,
> IdsX1 == 0.001(1 - (VinX1 - VgsX1)/(-1.5))^2}, {IdsX1}]
>
> Out[16]=
> {}
>
> What's going on? Why does a little algebra (the creation of the
> variable VgsX1) cause a problem? In[16] was generated by copying In[15]
> and doing some editing. No error messages were generated by either.
>
> Thanks,
>
> Joe Gwinn