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Eigenvalues of a linear transformation (Matrix)

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Iconate
#1
Nov4-09, 10:11 PM
P: 21
1. The problem statement, all variables and given/known data
Let T: M22 -> M22 be defined by
T[itex]

\[ \left( \begin{array}{cc}
a & b \\
c & d \\
\end{array} \right)\]

[/itex]=
[itex]

\[ \left( \begin{array}{cc}
2c & a+c \\
b-2c & d \\
\end{array} \right)\]

[/itex]

Find the eigenvectors of T



3. The attempt at a solution

My main question is, Which matrix am I using to compute my eigenvectors?
Do I need to compute a basis first?

Where this problem differs from my other questions is that I am no longer producing a matrix from my basis vectors which I use to create [T]B

Any insight would be great, thanks.
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Dick
#2
Nov4-09, 10:20 PM
Sci Advisor
HW Helper
Thanks
P: 25,251
M22 is a four dimensional vector space, right? A basis is e1=[[1,0],[0,0]], e2=[[0,1],[0,0]], e3=[[0,0],[1,0]] and e4=[[0,0],[0,1]], right? So T must be a 4x4 matrix in that basis, yes? Can you write out what it is in the {e1,e2,e3,e4} basis?
Iconate
#3
Nov4-09, 10:53 PM
P: 21
Yeah I did that, do I find the eigenvectors with each of their matricies?, normally id put my basis vectors INTO a matrix, but I have matricies, i figure they have to go somewhre, just dont know where

Dick
#4
Nov4-09, 11:00 PM
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P: 25,251
Eigenvalues of a linear transformation (Matrix)

I'm not sure I understand that. Just pretend [[a,b],[c,d]] is a 4 vector, [a,b,c,d]. T maps it to another 4 vector [2c,a+c,b-2c,d]. The fact they write these vectors as matrices is just a technicality.
Iconate
#5
Nov5-09, 02:29 PM
P: 21
I figured it out. I have to write T[e1] as a linear combination of the basis vectors.

Ex. T(e1) = [[0,1],[0,0]] = 0*e1 + 1*e2 + 0*e3 + 0*e4
= (0,1,0,0)

And Now i have my vector! Computing this for all ei's will create my matrix P.
Dick
#6
Nov5-09, 02:39 PM
Sci Advisor
HW Helper
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P: 25,251
Quote Quote by Iconate View Post
I figured it out. I have to write T[e1] as a linear combination of the basis vectors.

Ex. T(e1) = [[0,1],[0,0]] = 0*e1 + 1*e2 + 0*e3 + 0*e4
= (0,1,0,0)

And Now i have my vector! Computing this for all ei's will create my matrix P.
Exactly.


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