# Mutual Inductance - Mesh analysis

#### ydgmms

Joined Oct 6, 2007
10
I'm desperately trying to figure out this problem with ZERO luck.

I'm thinking its either my mesh equations or my calculating Vo after I obtain I2.

Mesh1 I get: 1*J1 + j6*J1 + j2*J2 = 10 angle 0
Mesh2 I get: j2*J1 + j4*J2 + 4*J2 - j3*J2 = 0

In Matrix(scilab input format, cuz I dont know how to do a matrix here)
a=[ 1+6j , 2j ; 2j , 4+j ]
b=[10;0]

So then, to calculate J1 and J2, I do

c=a/det(a)
c =

0.2416534 - 0.0206677i 0.0794913 + 0.0063593i
0.0794913 + 0.0063593i 0.0524642 - 0.1558029i

d=c*b
d =

2.4165342 - 0.2066773i
0.7949126 + 0.0635930i

Now I'm stuck here, getting my J2 into Vo. I try V=IR, so
d(2,1)*-3j =

ans =

0.1907790 - 2.3847377i

Which is not Vo according to the book...

Anyone? #### The Electrician

Joined Oct 9, 2007
2,848
Your problem is that the calculation c=a/det(a) does not give the inverse of a. Doesn't Scilab have a function like c = Inv(a) or c = Inverse(a)?

#### ydgmms

Joined Oct 6, 2007
10
The example problem I was trying to follow, had the coeffecient matrix over its determinate. ?

#### The Electrician

Joined Oct 9, 2007
2,848
If you will scan or photograph the page(s) from the example you're trying to follow and post them, I'll explain what they're doing.

In the meantime, if you will substitute c = inverse(a), (or whatever the correct syntax in Scilab is) instead of c = a/det(a), you will get the correct answer.

#### ydgmms

Joined Oct 6, 2007
10
If you will scan or photograph the page(s) from the example you're trying to follow and post them, I'll explain what they're doing.

In the meantime, if you will substitute c = inverse(a), (or whatever the correct syntax in Scilab is) instead of c = a/det(a), you will get the correct answer.
You are absolutely correct sir. I tried it with the way I SHOULD have the entire time. and within a minute I had the correct answer. Pissed me off to no end, i spent 2 hours last nite and i dunno how long monday and sunday nites.

i did c=a\b, then d=c(2,1)*-3j and got the proper Vo

Rich (BB code):
-->a
a  =

1. + 6.i    2.i
2.i         4. + i

-->b
b  =

10.
0.

-->c=a\b
c  =

0.5246423 - 1.5580286i
- 0.7949126 - 0.0635930i

-->c(2,1)*-3*%i
ans  =

- 0.1907790 + 2.3847377i

-->
And when I convert ans into a phasor, I get the proper Vo.

Thanks.. I dunno what the example problem and I were doing. #### The Electrician

Joined Oct 9, 2007
2,848
See the attachment for an explanation.

#### ydgmms

Joined Oct 6, 2007
10
See the attachment for an explanation.

Huh..interesting. I've never tried to figure out the inverse of a matrix by hand. Thats what threw me off. Never been taught it, always just been told 'use a calculator or MATLAB(scilab for us poor college students)'. So I thought they were doing something different when they had the matrix over its determinate.

I had noticed the sign change of the -j5 values. But thought it may be a misprint, as during the course we've seen a few in the book.

Oh well. Thanks for the explanation. I think I'll stick to scilab and how I normally solve coeffecient matrices.