Jordan canonical form of strictly upper or lower triangular matrices of even order n and rank n-1.

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I am trying to find the jordan canonical form of $
A=
left[ beginarraycccc
0 & 0 & 0 & 0 \
3 & 0 & 0 & 0 \
0 & 2 & 0 & 0 \
0 & 0 & 1 & 0 \
endarray right]
$.
In this process I found $0$ is the only eigen value with algebraic multiplicity $4$ and geometric multiplicity $1$ so jordan canonical form should have only one 0-jordan block of order $4$.
But as $A^3 = 0$, we have $x^3$ as minimal polynomial and that suggest the largest $0$-jordan block can be of order $3$.




Please help, where am I wrong?











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    up vote
    1
    down vote

    favorite












    I am trying to find the jordan canonical form of $
    A=
    left[ beginarraycccc
    0 & 0 & 0 & 0 \
    3 & 0 & 0 & 0 \
    0 & 2 & 0 & 0 \
    0 & 0 & 1 & 0 \
    endarray right]
    $.
    In this process I found $0$ is the only eigen value with algebraic multiplicity $4$ and geometric multiplicity $1$ so jordan canonical form should have only one 0-jordan block of order $4$.
    But as $A^3 = 0$, we have $x^3$ as minimal polynomial and that suggest the largest $0$-jordan block can be of order $3$.




    Please help, where am I wrong?











    share|cite|improve this question

























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      I am trying to find the jordan canonical form of $
      A=
      left[ beginarraycccc
      0 & 0 & 0 & 0 \
      3 & 0 & 0 & 0 \
      0 & 2 & 0 & 0 \
      0 & 0 & 1 & 0 \
      endarray right]
      $.
      In this process I found $0$ is the only eigen value with algebraic multiplicity $4$ and geometric multiplicity $1$ so jordan canonical form should have only one 0-jordan block of order $4$.
      But as $A^3 = 0$, we have $x^3$ as minimal polynomial and that suggest the largest $0$-jordan block can be of order $3$.




      Please help, where am I wrong?











      share|cite|improve this question















      I am trying to find the jordan canonical form of $
      A=
      left[ beginarraycccc
      0 & 0 & 0 & 0 \
      3 & 0 & 0 & 0 \
      0 & 2 & 0 & 0 \
      0 & 0 & 1 & 0 \
      endarray right]
      $.
      In this process I found $0$ is the only eigen value with algebraic multiplicity $4$ and geometric multiplicity $1$ so jordan canonical form should have only one 0-jordan block of order $4$.
      But as $A^3 = 0$, we have $x^3$ as minimal polynomial and that suggest the largest $0$-jordan block can be of order $3$.




      Please help, where am I wrong?








      linear-algebra linear-transformations






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      edited Sep 1 at 8:23









      Anonymous I

      8311726




      8311726










      asked Sep 1 at 7:53









      Voly op

      354




      354




















          1 Answer
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          octave:4> A
          A =

          0 0 0 0
          3 0 0 0
          0 2 0 0
          0 0 1 0

          octave:5> A^3
          ans =

          0 0 0 0
          0 0 0 0
          0 0 0 0
          6 0 0 0


          Notice at the lower left corner, the entry is non-zero. The minimal polynomial is indeed $x^4$.






          share|cite|improve this answer




















          • Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
            – Voly op
            Sep 1 at 8:10










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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          0
          down vote



          accepted










          octave:4> A
          A =

          0 0 0 0
          3 0 0 0
          0 2 0 0
          0 0 1 0

          octave:5> A^3
          ans =

          0 0 0 0
          0 0 0 0
          0 0 0 0
          6 0 0 0


          Notice at the lower left corner, the entry is non-zero. The minimal polynomial is indeed $x^4$.






          share|cite|improve this answer




















          • Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
            – Voly op
            Sep 1 at 8:10














          up vote
          0
          down vote



          accepted










          octave:4> A
          A =

          0 0 0 0
          3 0 0 0
          0 2 0 0
          0 0 1 0

          octave:5> A^3
          ans =

          0 0 0 0
          0 0 0 0
          0 0 0 0
          6 0 0 0


          Notice at the lower left corner, the entry is non-zero. The minimal polynomial is indeed $x^4$.






          share|cite|improve this answer




















          • Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
            – Voly op
            Sep 1 at 8:10












          up vote
          0
          down vote



          accepted







          up vote
          0
          down vote



          accepted






          octave:4> A
          A =

          0 0 0 0
          3 0 0 0
          0 2 0 0
          0 0 1 0

          octave:5> A^3
          ans =

          0 0 0 0
          0 0 0 0
          0 0 0 0
          6 0 0 0


          Notice at the lower left corner, the entry is non-zero. The minimal polynomial is indeed $x^4$.






          share|cite|improve this answer












          octave:4> A
          A =

          0 0 0 0
          3 0 0 0
          0 2 0 0
          0 0 1 0

          octave:5> A^3
          ans =

          0 0 0 0
          0 0 0 0
          0 0 0 0
          6 0 0 0


          Notice at the lower left corner, the entry is non-zero. The minimal polynomial is indeed $x^4$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Sep 1 at 8:01









          Siong Thye Goh

          81.9k1456104




          81.9k1456104











          • Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
            – Voly op
            Sep 1 at 8:10
















          • Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
            – Voly op
            Sep 1 at 8:10















          Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
          – Voly op
          Sep 1 at 8:10




          Ohh .. I calculated A^4 directly instead of A^3 and thought it was A^3. Poor me. Thank you.
          – Voly op
          Sep 1 at 8:10

















           

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