[sdiy] A little OT, Begging a hand

[Ian Fritz]

At 05:13 PM 2/8/2011, David G. Dixon wrote:
> > No, V1, V2, and V3 are applied voltages, as clearly stated in the original
> > problem.  And you finally have the right answer -- the problem cannot be
> > solved (because it is underdetermined).
>
>Yes, V1, V2 and V3 are the applied voltages.  However, in order to calculate
>the resistances, the voltages at all four nodes must be measured, including
>Vout.  If these node voltages are unknown, then the problem is not just
>underspecified; it is completely unstated.


That is wrong. All the current through R6 flows through R8.  They act as a 
single resistor as far as the system is concerned.  There is only one 
current at your so called node. Of course you need to measure V0, but you 
can do it after the system is solved, when you know the current through 
R8.  There are three nodes in the system and four unknowns.  If you want to 
include V0 in the system, then you have to add an extra equation.  In that 
case you have four equations and five unkn owns.

I've proved via the delta-wye transformation that the system is 
underdetermined.  Anyone who disagrees needs to either find an error in the 
proof or show the solution for the resistors.

Ian