finding the dimension of eigenspace with characteristic and minimal polynomial
I have a problem in understanding how author find the dimension of eigenspace of 3 and 1 in following example.
How can I calculate it?
For example, suppose you're given a $ 6 times 6 $
matrix and you calculate that its characteristic polynomial is $(t-3)^4(t-i)^2$, that
its minimal polynomial is $(t-3)^2 (t-i)^2$, that the 3-eigenspace is 3-dimensional,
and that the i-eigenspace is 1-dimensional.
Thanks for your help
linear-algebra matrices eigenvalues-eigenvectors
add a comment |
I have a problem in understanding how author find the dimension of eigenspace of 3 and 1 in following example.
How can I calculate it?
For example, suppose you're given a $ 6 times 6 $
matrix and you calculate that its characteristic polynomial is $(t-3)^4(t-i)^2$, that
its minimal polynomial is $(t-3)^2 (t-i)^2$, that the 3-eigenspace is 3-dimensional,
and that the i-eigenspace is 1-dimensional.
Thanks for your help
linear-algebra matrices eigenvalues-eigenvectors
add a comment |
I have a problem in understanding how author find the dimension of eigenspace of 3 and 1 in following example.
How can I calculate it?
For example, suppose you're given a $ 6 times 6 $
matrix and you calculate that its characteristic polynomial is $(t-3)^4(t-i)^2$, that
its minimal polynomial is $(t-3)^2 (t-i)^2$, that the 3-eigenspace is 3-dimensional,
and that the i-eigenspace is 1-dimensional.
Thanks for your help
linear-algebra matrices eigenvalues-eigenvectors
I have a problem in understanding how author find the dimension of eigenspace of 3 and 1 in following example.
How can I calculate it?
For example, suppose you're given a $ 6 times 6 $
matrix and you calculate that its characteristic polynomial is $(t-3)^4(t-i)^2$, that
its minimal polynomial is $(t-3)^2 (t-i)^2$, that the 3-eigenspace is 3-dimensional,
and that the i-eigenspace is 1-dimensional.
Thanks for your help
linear-algebra matrices eigenvalues-eigenvectors
linear-algebra matrices eigenvalues-eigenvectors
edited Dec 6 at 9:27
José Carlos Santos
148k22117218
148k22117218
asked Jun 13 '17 at 9:46
fateme jl
8710
8710
add a comment |
add a comment |
3 Answers
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Let us take for example the eigenvalue $;lambda=3;$: that the exponent of its linear factor in the minimal polynomial is two means that two is the largest block in the Jordan Block (=JB) corresponding to $;3;$, which means that the JB, which clearly has size $;4times4;$ , has exactly three blocks: one of size two, two of size one. Something like the following, with the different colors marking the different block in $;JB_3;$ :
$$JB_{lambda=3}=begin{pmatrix}
color{red}3&color{red}1&0&0\
color{red}0&color{red}3&0&0\
0&0&color{green}3&0\
0&0&0&color{blue}3end{pmatrix}$$
Since the number of blocks in $;JB_lambda;$ gives us $;dim V_lambda;$ ,we're done.
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
|
show 2 more comments
That implies its Jordan normal form is:
$begin{pmatrix}3&1&0&0&0&0\
0&3&0&0&0&0\
0&0&3&0&0&0\
0&0&0&3&0&0\
0&0&0&0&i&1\
0&0&0&0&0&iend{pmatrix}$
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
add a comment |
The Jordan form of your matrix must be of the type$$begin{pmatrix}3&*&0&0&0&0\0&3&*&0&0&0\0&0&3&*&0&0\0&0&0&3&0&0\0&0&0&0&i&*\0&0&0&0&0&iend{pmatrix},$$where each $*$ is either $0$ or $1$. But if, for instance, the $*$ from the fifth row is equal to $0$, then the exponent of $t-i$ in the minimal polynomial of the matrix must be $1$. Since it is $2$, that $*$ must be equal to $1$. Now, see what the other three $*$ must be so that the exponent of $t-3$ in the minimal polynomial of the matrix is $2$.
add a comment |
Your Answer
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3 Answers
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3 Answers
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Let us take for example the eigenvalue $;lambda=3;$: that the exponent of its linear factor in the minimal polynomial is two means that two is the largest block in the Jordan Block (=JB) corresponding to $;3;$, which means that the JB, which clearly has size $;4times4;$ , has exactly three blocks: one of size two, two of size one. Something like the following, with the different colors marking the different block in $;JB_3;$ :
$$JB_{lambda=3}=begin{pmatrix}
color{red}3&color{red}1&0&0\
color{red}0&color{red}3&0&0\
0&0&color{green}3&0\
0&0&0&color{blue}3end{pmatrix}$$
Since the number of blocks in $;JB_lambda;$ gives us $;dim V_lambda;$ ,we're done.
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
|
show 2 more comments
Let us take for example the eigenvalue $;lambda=3;$: that the exponent of its linear factor in the minimal polynomial is two means that two is the largest block in the Jordan Block (=JB) corresponding to $;3;$, which means that the JB, which clearly has size $;4times4;$ , has exactly three blocks: one of size two, two of size one. Something like the following, with the different colors marking the different block in $;JB_3;$ :
$$JB_{lambda=3}=begin{pmatrix}
color{red}3&color{red}1&0&0\
color{red}0&color{red}3&0&0\
0&0&color{green}3&0\
0&0&0&color{blue}3end{pmatrix}$$
Since the number of blocks in $;JB_lambda;$ gives us $;dim V_lambda;$ ,we're done.
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
|
show 2 more comments
Let us take for example the eigenvalue $;lambda=3;$: that the exponent of its linear factor in the minimal polynomial is two means that two is the largest block in the Jordan Block (=JB) corresponding to $;3;$, which means that the JB, which clearly has size $;4times4;$ , has exactly three blocks: one of size two, two of size one. Something like the following, with the different colors marking the different block in $;JB_3;$ :
$$JB_{lambda=3}=begin{pmatrix}
color{red}3&color{red}1&0&0\
color{red}0&color{red}3&0&0\
0&0&color{green}3&0\
0&0&0&color{blue}3end{pmatrix}$$
Since the number of blocks in $;JB_lambda;$ gives us $;dim V_lambda;$ ,we're done.
Let us take for example the eigenvalue $;lambda=3;$: that the exponent of its linear factor in the minimal polynomial is two means that two is the largest block in the Jordan Block (=JB) corresponding to $;3;$, which means that the JB, which clearly has size $;4times4;$ , has exactly three blocks: one of size two, two of size one. Something like the following, with the different colors marking the different block in $;JB_3;$ :
$$JB_{lambda=3}=begin{pmatrix}
color{red}3&color{red}1&0&0\
color{red}0&color{red}3&0&0\
0&0&color{green}3&0\
0&0&0&color{blue}3end{pmatrix}$$
Since the number of blocks in $;JB_lambda;$ gives us $;dim V_lambda;$ ,we're done.
answered Jun 13 '17 at 10:02
DonAntonio
176k1491225
176k1491225
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
|
show 2 more comments
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Isn't two Jordan blocks of size 2 a possibility?
– Rab
Jun 13 '17 at 10:05
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
Cause the minimal polynomial exponent is the largest JB, but I could be wrong, I am still studying it in uni.
– Rab
Jun 13 '17 at 10:10
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
@RabMakh You're completely correct, but in this case we're given that $;dim V_3=3;$ , so there can't be only two blocks but three.
– DonAntonio
Jun 13 '17 at 11:20
1
1
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
Hmm...wait, re-reading your question, the eigenspace's dimension is not given, right? If so, then there exist two possibilities, indeed: what I wrote and two $';2times2;$ blocks, I believe.
– DonAntonio
Jun 13 '17 at 11:22
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
@DonAntonio "3-eigenspace is 3-dimensional", it is given ...
– Peter Melech
Jun 16 '17 at 7:52
|
show 2 more comments
That implies its Jordan normal form is:
$begin{pmatrix}3&1&0&0&0&0\
0&3&0&0&0&0\
0&0&3&0&0&0\
0&0&0&3&0&0\
0&0&0&0&i&1\
0&0&0&0&0&iend{pmatrix}$
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
add a comment |
That implies its Jordan normal form is:
$begin{pmatrix}3&1&0&0&0&0\
0&3&0&0&0&0\
0&0&3&0&0&0\
0&0&0&3&0&0\
0&0&0&0&i&1\
0&0&0&0&0&iend{pmatrix}$
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
add a comment |
That implies its Jordan normal form is:
$begin{pmatrix}3&1&0&0&0&0\
0&3&0&0&0&0\
0&0&3&0&0&0\
0&0&0&3&0&0\
0&0&0&0&i&1\
0&0&0&0&0&iend{pmatrix}$
That implies its Jordan normal form is:
$begin{pmatrix}3&1&0&0&0&0\
0&3&0&0&0&0\
0&0&3&0&0&0\
0&0&0&3&0&0\
0&0&0&0&i&1\
0&0&0&0&0&iend{pmatrix}$
answered Jun 13 '17 at 10:06
Peter Melech
2,529813
2,529813
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
add a comment |
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
why we don't have two 2*2 blocks for eigenvalue 3?
– fateme jl
Jun 15 '17 at 12:05
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
Because the dimension of the eigenspace is 3, there must be three Jordan blocks, each one containing one entry corresponding to an eigenvector, because of the exponent 2 in the minimal polynomial the first block is 2*2, the remaining blocks must be 1*1
– Peter Melech
Jun 16 '17 at 7:48
add a comment |
The Jordan form of your matrix must be of the type$$begin{pmatrix}3&*&0&0&0&0\0&3&*&0&0&0\0&0&3&*&0&0\0&0&0&3&0&0\0&0&0&0&i&*\0&0&0&0&0&iend{pmatrix},$$where each $*$ is either $0$ or $1$. But if, for instance, the $*$ from the fifth row is equal to $0$, then the exponent of $t-i$ in the minimal polynomial of the matrix must be $1$. Since it is $2$, that $*$ must be equal to $1$. Now, see what the other three $*$ must be so that the exponent of $t-3$ in the minimal polynomial of the matrix is $2$.
add a comment |
The Jordan form of your matrix must be of the type$$begin{pmatrix}3&*&0&0&0&0\0&3&*&0&0&0\0&0&3&*&0&0\0&0&0&3&0&0\0&0&0&0&i&*\0&0&0&0&0&iend{pmatrix},$$where each $*$ is either $0$ or $1$. But if, for instance, the $*$ from the fifth row is equal to $0$, then the exponent of $t-i$ in the minimal polynomial of the matrix must be $1$. Since it is $2$, that $*$ must be equal to $1$. Now, see what the other three $*$ must be so that the exponent of $t-3$ in the minimal polynomial of the matrix is $2$.
add a comment |
The Jordan form of your matrix must be of the type$$begin{pmatrix}3&*&0&0&0&0\0&3&*&0&0&0\0&0&3&*&0&0\0&0&0&3&0&0\0&0&0&0&i&*\0&0&0&0&0&iend{pmatrix},$$where each $*$ is either $0$ or $1$. But if, for instance, the $*$ from the fifth row is equal to $0$, then the exponent of $t-i$ in the minimal polynomial of the matrix must be $1$. Since it is $2$, that $*$ must be equal to $1$. Now, see what the other three $*$ must be so that the exponent of $t-3$ in the minimal polynomial of the matrix is $2$.
The Jordan form of your matrix must be of the type$$begin{pmatrix}3&*&0&0&0&0\0&3&*&0&0&0\0&0&3&*&0&0\0&0&0&3&0&0\0&0&0&0&i&*\0&0&0&0&0&iend{pmatrix},$$where each $*$ is either $0$ or $1$. But if, for instance, the $*$ from the fifth row is equal to $0$, then the exponent of $t-i$ in the minimal polynomial of the matrix must be $1$. Since it is $2$, that $*$ must be equal to $1$. Now, see what the other three $*$ must be so that the exponent of $t-3$ in the minimal polynomial of the matrix is $2$.
answered Jun 13 '17 at 10:08
José Carlos Santos
148k22117218
148k22117218
add a comment |
add a comment |
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