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Why is a matrix multiplied by an eigenvector not parallel to that eigenvector?


Eigenvalue and Eigenvector for the change of Basis MatrixUnder what conditions does a complex matrix with a real eigenvalue have a corresponding real eigenvector?An eigenvector is a non-zero vector such that…Proof that eigenvector corresponding to simple eigenvalue is continuousPlease help with the rank-1 matrix eigenvectoreigenvector equivalence for subspace of matrix?If every non-zero vectors be the eigenvector of a real matrix $A$, prove that $A$ is the scalar matrix $lambda I_n$.Finding a vector that is not an eigenvector of a matrixEigenvector and adjoint eigenvector not orthogonalProve that any non zero linear combination of two eigenvectors is also an eigenvector













0












$begingroup$


If $lambda$ is a non-zero eigenvalue with a corresponding eigenvector $v$, then $A v$ is parallel to $v$.



This statement is false. Why is that? Would it be parallel to $lambda v$?










share|cite|improve this question











$endgroup$







  • 2




    $begingroup$
    What is your definition of parallel?
    $endgroup$
    – Brian Fitzpatrick
    Mar 11 at 2:23






  • 1




    $begingroup$
    What are your definitions of eigenvector and eigenvalue?
    $endgroup$
    – Brian Borchers
    Mar 11 at 2:27










  • $begingroup$
    If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
    $endgroup$
    – Sebastian Cor
    Mar 11 at 3:05






  • 2




    $begingroup$
    What makes you think the statement is false, Samurai? Can you show us a counterexample?
    $endgroup$
    – Gerry Myerson
    Mar 11 at 4:05






  • 2




    $begingroup$
    The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
    $endgroup$
    – user1551
    Mar 11 at 8:55
















0












$begingroup$


If $lambda$ is a non-zero eigenvalue with a corresponding eigenvector $v$, then $A v$ is parallel to $v$.



This statement is false. Why is that? Would it be parallel to $lambda v$?










share|cite|improve this question











$endgroup$







  • 2




    $begingroup$
    What is your definition of parallel?
    $endgroup$
    – Brian Fitzpatrick
    Mar 11 at 2:23






  • 1




    $begingroup$
    What are your definitions of eigenvector and eigenvalue?
    $endgroup$
    – Brian Borchers
    Mar 11 at 2:27










  • $begingroup$
    If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
    $endgroup$
    – Sebastian Cor
    Mar 11 at 3:05






  • 2




    $begingroup$
    What makes you think the statement is false, Samurai? Can you show us a counterexample?
    $endgroup$
    – Gerry Myerson
    Mar 11 at 4:05






  • 2




    $begingroup$
    The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
    $endgroup$
    – user1551
    Mar 11 at 8:55














0












0








0





$begingroup$


If $lambda$ is a non-zero eigenvalue with a corresponding eigenvector $v$, then $A v$ is parallel to $v$.



This statement is false. Why is that? Would it be parallel to $lambda v$?










share|cite|improve this question











$endgroup$




If $lambda$ is a non-zero eigenvalue with a corresponding eigenvector $v$, then $A v$ is parallel to $v$.



This statement is false. Why is that? Would it be parallel to $lambda v$?







linear-algebra eigenfunctions






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 11 at 8:51









Rodrigo de Azevedo

13k41960




13k41960










asked Mar 11 at 2:20









Samurai BaleSamurai Bale

645




645







  • 2




    $begingroup$
    What is your definition of parallel?
    $endgroup$
    – Brian Fitzpatrick
    Mar 11 at 2:23






  • 1




    $begingroup$
    What are your definitions of eigenvector and eigenvalue?
    $endgroup$
    – Brian Borchers
    Mar 11 at 2:27










  • $begingroup$
    If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
    $endgroup$
    – Sebastian Cor
    Mar 11 at 3:05






  • 2




    $begingroup$
    What makes you think the statement is false, Samurai? Can you show us a counterexample?
    $endgroup$
    – Gerry Myerson
    Mar 11 at 4:05






  • 2




    $begingroup$
    The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
    $endgroup$
    – user1551
    Mar 11 at 8:55













  • 2




    $begingroup$
    What is your definition of parallel?
    $endgroup$
    – Brian Fitzpatrick
    Mar 11 at 2:23






  • 1




    $begingroup$
    What are your definitions of eigenvector and eigenvalue?
    $endgroup$
    – Brian Borchers
    Mar 11 at 2:27










  • $begingroup$
    If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
    $endgroup$
    – Sebastian Cor
    Mar 11 at 3:05






  • 2




    $begingroup$
    What makes you think the statement is false, Samurai? Can you show us a counterexample?
    $endgroup$
    – Gerry Myerson
    Mar 11 at 4:05






  • 2




    $begingroup$
    The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
    $endgroup$
    – user1551
    Mar 11 at 8:55








2




2




$begingroup$
What is your definition of parallel?
$endgroup$
– Brian Fitzpatrick
Mar 11 at 2:23




$begingroup$
What is your definition of parallel?
$endgroup$
– Brian Fitzpatrick
Mar 11 at 2:23




1




1




$begingroup$
What are your definitions of eigenvector and eigenvalue?
$endgroup$
– Brian Borchers
Mar 11 at 2:27




$begingroup$
What are your definitions of eigenvector and eigenvalue?
$endgroup$
– Brian Borchers
Mar 11 at 2:27












$begingroup$
If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
$endgroup$
– Sebastian Cor
Mar 11 at 3:05




$begingroup$
If $vecvin S_lambda$ $Avecvcdotvecv=lambdavecvcdotvecv=lambda||vecv||^2=1 iff ||vecv||^2=dfrac1lambda$
$endgroup$
– Sebastian Cor
Mar 11 at 3:05




2




2




$begingroup$
What makes you think the statement is false, Samurai? Can you show us a counterexample?
$endgroup$
– Gerry Myerson
Mar 11 at 4:05




$begingroup$
What makes you think the statement is false, Samurai? Can you show us a counterexample?
$endgroup$
– Gerry Myerson
Mar 11 at 4:05




2




2




$begingroup$
The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
$endgroup$
– user1551
Mar 11 at 8:55





$begingroup$
The only explantions that I can come up with are: (1) it's a calculation mistake, (2) perhaps $lambda=0$ and in someone's definition, two vectors are said to be parallel only if they are scalar multiples of each other (this is just a wild guess; personally, I treat $0$ as a vector that is parallel to every vector).
$endgroup$
– user1551
Mar 11 at 8:55











1 Answer
1






active

oldest

votes


















1












$begingroup$

It's hard to know what to make of your question as you didn't specify what matrix $vecv$ is an eigenvector of.
If $A$ were the matrix corresponding to that eigenvector, then $Avecv=lambdavecv$, by definition, meaning the statement would be true. Since you're sure the statement is false, then we can assume that $A$ is not the matrix corresponding to that eigenvector. In that case, of course, $Avecv$ need not equal $lambda vecv$.
If you're confused about what it means to be parallel or what an Eigenvector is, I recommend 3b1b's video on the topic.






share|cite|improve this answer









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    $begingroup$

    It's hard to know what to make of your question as you didn't specify what matrix $vecv$ is an eigenvector of.
    If $A$ were the matrix corresponding to that eigenvector, then $Avecv=lambdavecv$, by definition, meaning the statement would be true. Since you're sure the statement is false, then we can assume that $A$ is not the matrix corresponding to that eigenvector. In that case, of course, $Avecv$ need not equal $lambda vecv$.
    If you're confused about what it means to be parallel or what an Eigenvector is, I recommend 3b1b's video on the topic.






    share|cite|improve this answer









    $endgroup$

















      1












      $begingroup$

      It's hard to know what to make of your question as you didn't specify what matrix $vecv$ is an eigenvector of.
      If $A$ were the matrix corresponding to that eigenvector, then $Avecv=lambdavecv$, by definition, meaning the statement would be true. Since you're sure the statement is false, then we can assume that $A$ is not the matrix corresponding to that eigenvector. In that case, of course, $Avecv$ need not equal $lambda vecv$.
      If you're confused about what it means to be parallel or what an Eigenvector is, I recommend 3b1b's video on the topic.






      share|cite|improve this answer









      $endgroup$















        1












        1








        1





        $begingroup$

        It's hard to know what to make of your question as you didn't specify what matrix $vecv$ is an eigenvector of.
        If $A$ were the matrix corresponding to that eigenvector, then $Avecv=lambdavecv$, by definition, meaning the statement would be true. Since you're sure the statement is false, then we can assume that $A$ is not the matrix corresponding to that eigenvector. In that case, of course, $Avecv$ need not equal $lambda vecv$.
        If you're confused about what it means to be parallel or what an Eigenvector is, I recommend 3b1b's video on the topic.






        share|cite|improve this answer









        $endgroup$



        It's hard to know what to make of your question as you didn't specify what matrix $vecv$ is an eigenvector of.
        If $A$ were the matrix corresponding to that eigenvector, then $Avecv=lambdavecv$, by definition, meaning the statement would be true. Since you're sure the statement is false, then we can assume that $A$ is not the matrix corresponding to that eigenvector. In that case, of course, $Avecv$ need not equal $lambda vecv$.
        If you're confused about what it means to be parallel or what an Eigenvector is, I recommend 3b1b's video on the topic.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Mar 11 at 8:45









        PatrickPatrick

        1018




        1018



























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