Re: Solve[] handles the same system differently
- To: mathgroup at smc.vnet.net
- Subject: [mg40851] Re: Solve[] handles the same system differently
- From: Raibatak Das <rd54 at cornell.edu>
- Date: Tue, 22 Apr 2003 06:43:41 -0400 (EDT)
- References: <b80k0i$m3f$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
jg -
what you are attempting to do in the second case is to eliminate the
variable VgsX1 from the final solution and you should specify that as
the third option in the Solve command as shown below.
In[1]:=
Solve[{Rx==3300,VinX1==0,
IdsX1==0.001(1-(VinX1-Rx*IdsX1)/(-1.5))^2},{IdsX1}]
Out[1]=
{{IdsX1->0.000234453},{IdsX1->0.00088125}}
In[2]:=
Solve[{Rx==3300,VinX1==0,
IdsX1==0.001(1-(VinX1-VgsX1)/(-1.5))^2,
VgsX1==Rx*IdsX1},IdsX1,VgsX1]
Out[2]=
{{IdsX1->0.000234453},{IdsX1->0.00088125}}
- rd.
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
>
>
------------------------------------------------------------------------
* /Raibatak Das / *
Department of Chemistry and Chemical Biology, Cornell University.
Ithaca, NY 14853.
Ph : 1-607-255-6141
email : rd54 at cornell.edu <mailto:rd54 at cornell.edu>