# matrix problem

#### ees1

Joined Jan 7, 2008
37
One of my lecture notes showing a 3x3 matrix, let's name this matrix Y.
I am confused about the result Y^-1.
I am trying to find some study material for relating to Y^-1, and I couldn't find any useful information(actually I still don't know how professor got his answer)
I guess the material I studied wasn't right. Could anyone can provide the searching key words for learning this related subject?

#### Papabravo

Joined Feb 24, 2006
14,205
Sure, Y^-1 is the inverse of Y. When you multiply the two matricies together you get the Identity matrix
Rich (BB code):
Y*Y^-1 = I = [ 1 0 0 ; 0 1 0 ; 0 0 1]
Many software packages like Matlab, Scilab, and R will give you the inverse of a 3 x 3 matrix in the twinkling of an eye. I've heard tell that inverting one by hand is possible by using minors and cofactors but I haven't done it recently. Inverting a 4 x 4 or larger is definitely not -- you'll excuse the expression -- a hand job.

#### ees1

Joined Jan 7, 2008
37
thank you. I think I will use the TI caculator instead.

#### Dave

Joined Nov 17, 2003
6,970
Many software packages like Matlab, Scilab, and R will give you the inverse of a 3 x 3 matrix in the twinkling of an eye. I've heard tell that inverting one by hand is possible by using minors and cofactors but I haven't done it recently. Inverting a 4 x 4 or larger is definitely not -- you'll excuse the expression -- a hand job.
PB, I recall the manual approach was quite laborious. You are right to suggest numerical packages like Matlab, which is expensive, so look at one of the matrix-based (free) alternatives: http://forum.allaboutcircuits.com/blog.php?b=65

Dave

#### Papabravo

Joined Feb 24, 2006
14,205

#### hgmjr

Joined Jan 28, 2005
9,029
Don't overlook the fact that Microsoft EXCEL has a matrix function that can be used to perform matrix manipulation.

hgmjr