finding geometric multiplicity of a given matrix












1












$begingroup$


Let



$A =begin{bmatrix} a & 2f & 0 \ 2f & b & 3f \ 0 & 3f & c end{bmatrix}, tag 1$



where $a, b, c, f$ are real numbers and $f ne 0$. What is the geometric multiplicity of the largest eigenvalue of $A$?



For a symmetric matrix the geometric multiplicity equals algebraic multiplicity,so we can check the eigen values of the matrix but I find that difficult to solve. Is there any different approach to this problem ? Can anyone give some idea.
Thanks in advance.










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$endgroup$












  • $begingroup$
    I edited your post to $LaTeX$ify it properly. Cheers!
    $endgroup$
    – Robert Lewis
    Dec 18 '18 at 17:51
















1












$begingroup$


Let



$A =begin{bmatrix} a & 2f & 0 \ 2f & b & 3f \ 0 & 3f & c end{bmatrix}, tag 1$



where $a, b, c, f$ are real numbers and $f ne 0$. What is the geometric multiplicity of the largest eigenvalue of $A$?



For a symmetric matrix the geometric multiplicity equals algebraic multiplicity,so we can check the eigen values of the matrix but I find that difficult to solve. Is there any different approach to this problem ? Can anyone give some idea.
Thanks in advance.










share|cite|improve this question











$endgroup$












  • $begingroup$
    I edited your post to $LaTeX$ify it properly. Cheers!
    $endgroup$
    – Robert Lewis
    Dec 18 '18 at 17:51














1












1








1





$begingroup$


Let



$A =begin{bmatrix} a & 2f & 0 \ 2f & b & 3f \ 0 & 3f & c end{bmatrix}, tag 1$



where $a, b, c, f$ are real numbers and $f ne 0$. What is the geometric multiplicity of the largest eigenvalue of $A$?



For a symmetric matrix the geometric multiplicity equals algebraic multiplicity,so we can check the eigen values of the matrix but I find that difficult to solve. Is there any different approach to this problem ? Can anyone give some idea.
Thanks in advance.










share|cite|improve this question











$endgroup$




Let



$A =begin{bmatrix} a & 2f & 0 \ 2f & b & 3f \ 0 & 3f & c end{bmatrix}, tag 1$



where $a, b, c, f$ are real numbers and $f ne 0$. What is the geometric multiplicity of the largest eigenvalue of $A$?



For a symmetric matrix the geometric multiplicity equals algebraic multiplicity,so we can check the eigen values of the matrix but I find that difficult to solve. Is there any different approach to this problem ? Can anyone give some idea.
Thanks in advance.







linear-algebra






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share|cite|improve this question













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share|cite|improve this question








edited Dec 18 '18 at 17:48









Robert Lewis

48.1k23167




48.1k23167










asked Dec 18 '18 at 17:01









math mathmath math

186




186












  • $begingroup$
    I edited your post to $LaTeX$ify it properly. Cheers!
    $endgroup$
    – Robert Lewis
    Dec 18 '18 at 17:51


















  • $begingroup$
    I edited your post to $LaTeX$ify it properly. Cheers!
    $endgroup$
    – Robert Lewis
    Dec 18 '18 at 17:51
















$begingroup$
I edited your post to $LaTeX$ify it properly. Cheers!
$endgroup$
– Robert Lewis
Dec 18 '18 at 17:51




$begingroup$
I edited your post to $LaTeX$ify it properly. Cheers!
$endgroup$
– Robert Lewis
Dec 18 '18 at 17:51










3 Answers
3






active

oldest

votes


















0












$begingroup$

Hint: If we can show that the matrix has distinct eigenvalues then, we can say that the geometric multiplicity of the largest eigen value is 1.






share|cite|improve this answer









$endgroup$





















    0












    $begingroup$

    Hint: If $lambda$ has the geometric multiplicity of $n,$ then
    $$
    begin{bmatrix}
    a-lambda & 2f & 0 \
    2f & b-lambda & 3f \
    0 & 3f & c-lambda
    end{bmatrix}
    $$

    has the rank $3-n.$



    A rank of $1$ means that each row (or each column) is a multiple of the same vector.



    A rank of $0$ means that the matrix is the zero-matrix.



    Can any of these happen?






    share|cite|improve this answer









    $endgroup$





















      0












      $begingroup$

      As you claimed, the matrix is symmetric hence diagonalizable, and thus is the geometric multiplicity of any eigenvalue equal to its algebraic multiplicity.



      If all $a,b,c,f$ are positive, by Perron-Frobenius theorem is the eigenvalue with the largest absolute value real and positive, and is simple (multiplicity 1). In other words, the spectral radius of the matrix is also an eigenvalue.






      share|cite|improve this answer









      $endgroup$













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        3 Answers
        3






        active

        oldest

        votes








        3 Answers
        3






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        0












        $begingroup$

        Hint: If we can show that the matrix has distinct eigenvalues then, we can say that the geometric multiplicity of the largest eigen value is 1.






        share|cite|improve this answer









        $endgroup$


















          0












          $begingroup$

          Hint: If we can show that the matrix has distinct eigenvalues then, we can say that the geometric multiplicity of the largest eigen value is 1.






          share|cite|improve this answer









          $endgroup$
















            0












            0








            0





            $begingroup$

            Hint: If we can show that the matrix has distinct eigenvalues then, we can say that the geometric multiplicity of the largest eigen value is 1.






            share|cite|improve this answer









            $endgroup$



            Hint: If we can show that the matrix has distinct eigenvalues then, we can say that the geometric multiplicity of the largest eigen value is 1.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Jan 2 at 12:29









            shreyas s rshreyas s r

            1




            1























                0












                $begingroup$

                Hint: If $lambda$ has the geometric multiplicity of $n,$ then
                $$
                begin{bmatrix}
                a-lambda & 2f & 0 \
                2f & b-lambda & 3f \
                0 & 3f & c-lambda
                end{bmatrix}
                $$

                has the rank $3-n.$



                A rank of $1$ means that each row (or each column) is a multiple of the same vector.



                A rank of $0$ means that the matrix is the zero-matrix.



                Can any of these happen?






                share|cite|improve this answer









                $endgroup$


















                  0












                  $begingroup$

                  Hint: If $lambda$ has the geometric multiplicity of $n,$ then
                  $$
                  begin{bmatrix}
                  a-lambda & 2f & 0 \
                  2f & b-lambda & 3f \
                  0 & 3f & c-lambda
                  end{bmatrix}
                  $$

                  has the rank $3-n.$



                  A rank of $1$ means that each row (or each column) is a multiple of the same vector.



                  A rank of $0$ means that the matrix is the zero-matrix.



                  Can any of these happen?






                  share|cite|improve this answer









                  $endgroup$
















                    0












                    0








                    0





                    $begingroup$

                    Hint: If $lambda$ has the geometric multiplicity of $n,$ then
                    $$
                    begin{bmatrix}
                    a-lambda & 2f & 0 \
                    2f & b-lambda & 3f \
                    0 & 3f & c-lambda
                    end{bmatrix}
                    $$

                    has the rank $3-n.$



                    A rank of $1$ means that each row (or each column) is a multiple of the same vector.



                    A rank of $0$ means that the matrix is the zero-matrix.



                    Can any of these happen?






                    share|cite|improve this answer









                    $endgroup$



                    Hint: If $lambda$ has the geometric multiplicity of $n,$ then
                    $$
                    begin{bmatrix}
                    a-lambda & 2f & 0 \
                    2f & b-lambda & 3f \
                    0 & 3f & c-lambda
                    end{bmatrix}
                    $$

                    has the rank $3-n.$



                    A rank of $1$ means that each row (or each column) is a multiple of the same vector.



                    A rank of $0$ means that the matrix is the zero-matrix.



                    Can any of these happen?







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered Jan 2 at 15:35









                    Reinhard MeierReinhard Meier

                    2,912310




                    2,912310























                        0












                        $begingroup$

                        As you claimed, the matrix is symmetric hence diagonalizable, and thus is the geometric multiplicity of any eigenvalue equal to its algebraic multiplicity.



                        If all $a,b,c,f$ are positive, by Perron-Frobenius theorem is the eigenvalue with the largest absolute value real and positive, and is simple (multiplicity 1). In other words, the spectral radius of the matrix is also an eigenvalue.






                        share|cite|improve this answer









                        $endgroup$


















                          0












                          $begingroup$

                          As you claimed, the matrix is symmetric hence diagonalizable, and thus is the geometric multiplicity of any eigenvalue equal to its algebraic multiplicity.



                          If all $a,b,c,f$ are positive, by Perron-Frobenius theorem is the eigenvalue with the largest absolute value real and positive, and is simple (multiplicity 1). In other words, the spectral radius of the matrix is also an eigenvalue.






                          share|cite|improve this answer









                          $endgroup$
















                            0












                            0








                            0





                            $begingroup$

                            As you claimed, the matrix is symmetric hence diagonalizable, and thus is the geometric multiplicity of any eigenvalue equal to its algebraic multiplicity.



                            If all $a,b,c,f$ are positive, by Perron-Frobenius theorem is the eigenvalue with the largest absolute value real and positive, and is simple (multiplicity 1). In other words, the spectral radius of the matrix is also an eigenvalue.






                            share|cite|improve this answer









                            $endgroup$



                            As you claimed, the matrix is symmetric hence diagonalizable, and thus is the geometric multiplicity of any eigenvalue equal to its algebraic multiplicity.



                            If all $a,b,c,f$ are positive, by Perron-Frobenius theorem is the eigenvalue with the largest absolute value real and positive, and is simple (multiplicity 1). In other words, the spectral radius of the matrix is also an eigenvalue.







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered Jan 2 at 23:24









                            user376343user376343

                            3,9584829




                            3,9584829






























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