# Nodal Analysis

1. Oct 2, 2009

### smithc2005

1. The problem statement, all variables and given/known data
I have to solve for V0 , using nodal analysis. I am getting different answers in matlab and PSPICE. The circuit is below

2 supernodes ; or 1 big supernode Here are my nodal equations:

v1-v3 = 12
v3 - v2 = 6

(v3)/6k + (v1)/4k - 6/k = 0

Matlab output is here:

Code (Text):
A=[1,0,-1;0,-1,1;.004,0,.006]
b=[12;6;.006]
format long
inv(A)*b

A =

1.0000         0   -1.0000
0   -1.0000    1.0000
0.0040         0    0.0060

b =

12.0000
6.0000
0.0060

ans =

7.799999999999999
-10.200000000000001
-4.200000000000001
PSPICE Schematic:

So confused!!!!

2. Relevant equations
I = V/R

3. The attempt at a solution
I have gotten -4.2 from matlab and 7.2 from pspice.

2. Oct 2, 2009

### mplayer

Try grounding the node connected to 2 voltage sources. This will simplify the analysis by only having to solve for a single node voltage.

3. Oct 3, 2009

### viscousflow

I have solved this by hand and I can tell you that your equations, and pspice are correct.

I just wonder about what it is you're 'saying' by that matlab code, I will have to look at it in more depth.

4. Nov 6, 2009

### Abha

Clearly the Matlab answer is wrong since it does not satisfy the III equation:

(v3)/6k + (v1)/4k = -4.2/6k + 7.8/4k = -.7/k + 1.9/k =1.2/k != 6/k

On closer inspection, you will see that the conversion from
(v3)/6k + (v1)/4k - 6/k = 0
to
A=[1,0,-1;0,-1,1;.004,0,.006] is erroneous -
1/4k != .004, 1/6k != .006

I suppose you already figured it out by now.. anyhow it may help someone who reads the thread.

Cheers,
Abha