CHAPTER 10.08: EIGENVALUES AND
EIGENVECTORS: Theorems of eigenvalues and eigenvectors Part 1 of 6 In
this segment we will talk about some of the theorems which are related to eigenvalues
and eigenvectors so one of the first theorems which people talk about is if
[A] is a square matrix (nxn) but it is upper
triangular, lower triangular or diagonal matrix, then the eigenvalues of [A]
are the diagonal entries of [A] so if you have an upper triangular matrix or
lower triangular matrix or a diagonal matrix then you will find out the
eigenvalues of [A] you don’t have to go through the process of finding the
determinant and things like that because the eigenvalues of [A] themselves are
the diagonal entries of the [A] matrix so let’s take an example if somebody
gives you a lower triangular matrix like this [A]= 6, 0, 0, 3, -2, 0, 7, 6, 5
so this is a lower triangular matrix because anything above the diagonal is
zero so that’s a lower triangular matrix since every element above the
diagonal is zero and in this case the three eigenvalues which you will get
for this particular upper triangular matrix will lower triangular matrix will
be λ1= 6, λ2= -2, λ3= 5 so from this lower triangular matrix
you have three eigenvalues λ1= 6, λ2= -2, λ3= 5 and that is
the end of this segment n this segment we will talk
about what does the word eigenvalue itself mean eigenvalue comes from the
word Eigenwert it is a general word and this “Eigen” stands for
characteristic and then this one the word “wert” here stands for value so
that’s where the origin of the word eigenvalue comes from characteristic value
it will make sense later when you when we talk about eigenvalues how we find
eigenvalues what we are do is finding something called the characteristic
polynomial of which we have to find the zeros of or take the take the
characteristic polynomial put it equal to zero and of that equation we have to find
the roots so that’s what the word eigenvalue comes from and that’s the end of
this segment. |