Re: Solve[] handles the same system differently
- To: mathgroup at smc.vnet.net
- Subject: [mg40861] Re: Solve[] handles the same system differently
- From: "Peter Pein" <peter1963 at totalise.co.uk>
- Date: Tue, 22 Apr 2003 06:47:00 -0400 (EDT)
- References: <b80k0i$m3f$1@smc.vnet.net>
- Reply-to: "Peter Pein" <peter1963 at totalise.co.uk>
- Sender: owner-wri-mathgroup at wolfram.com
"Joe Gwinn" <joegwinn at attbi.com> schrieb im Newsbeitrag news:b80k0i$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]= > {} > > > 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 > Hi Joe, I guess this happens due to the two values for VgsX1. So the algorithm can not "really eliminate" this var. Perhaps somebody really knows, what's going on. Solve[{Rx == 3300, VinX1 == 0, VgsX1 == Rx*IdsX1, IdsX1 == 0.001*(1 - (VinX1 - VgsX1)/(-3/2))^2}, {IdsX1, VgsX1}] gives {{IdsX1 -> 0.00023445297846077417, VgsX1 -> 0.7736948289205547}, {IdsX1 -> 0.0008812495008780689, VgsX1 -> 2.9081233528976274}} Peter