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Re: Solve[] handles the same system differently

  • To: mathgroup at smc.vnet.net
  • Subject: [mg40858] Re: Solve[] handles the same system differently
  • From: "Bill Bertram" <wkb at ansto.gov.au>
  • Date: Tue, 22 Apr 2003 06:46:35 -0400 (EDT)
  • Organization: Australian Nuclear Science and Technology Organisation
  • References: <b80k0i$m3f$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Joe Gwinn" <joegwinn at attbi.com> wrote in message
news:b80k0i$m3f$1 at smc.vnet.net...
> 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]=
> {}

Hi Joe,

Your second system is now contains two unknowns, the easiest way to fix it
is by changinge the final bracket {IdsX1} to {IdsX1,VgsX1}.

Cheers,
 Bill




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