Similar/Equivalent matrices and field extensions












2












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Let $F$ be a field and $F' supseteq F$ be a field extension. Suppose $A, B in M_n(F)$ are equivalent in $M_n(F')$, so there exist $P, Q in GL_n(F')$ such that $A = PBQ$. Is it necessarily true that $A$ and $B$ are equivalent in $M_n(F)$?



How about if "equivalent" is replaced with "similar"?










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  • 1




    $begingroup$
    For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:43






  • 1




    $begingroup$
    For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:44










  • $begingroup$
    Thanks for the replies! Very helpful.
    $endgroup$
    – Jeremiah Goertz
    Dec 5 '18 at 1:52
















2












$begingroup$


Let $F$ be a field and $F' supseteq F$ be a field extension. Suppose $A, B in M_n(F)$ are equivalent in $M_n(F')$, so there exist $P, Q in GL_n(F')$ such that $A = PBQ$. Is it necessarily true that $A$ and $B$ are equivalent in $M_n(F)$?



How about if "equivalent" is replaced with "similar"?










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:43






  • 1




    $begingroup$
    For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:44










  • $begingroup$
    Thanks for the replies! Very helpful.
    $endgroup$
    – Jeremiah Goertz
    Dec 5 '18 at 1:52














2












2








2


1



$begingroup$


Let $F$ be a field and $F' supseteq F$ be a field extension. Suppose $A, B in M_n(F)$ are equivalent in $M_n(F')$, so there exist $P, Q in GL_n(F')$ such that $A = PBQ$. Is it necessarily true that $A$ and $B$ are equivalent in $M_n(F)$?



How about if "equivalent" is replaced with "similar"?










share|cite|improve this question









$endgroup$




Let $F$ be a field and $F' supseteq F$ be a field extension. Suppose $A, B in M_n(F)$ are equivalent in $M_n(F')$, so there exist $P, Q in GL_n(F')$ such that $A = PBQ$. Is it necessarily true that $A$ and $B$ are equivalent in $M_n(F)$?



How about if "equivalent" is replaced with "similar"?







linear-algebra abstract-algebra






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 4 '18 at 0:12









Jeremiah GoertzJeremiah Goertz

313




313








  • 1




    $begingroup$
    For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:43






  • 1




    $begingroup$
    For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:44










  • $begingroup$
    Thanks for the replies! Very helpful.
    $endgroup$
    – Jeremiah Goertz
    Dec 5 '18 at 1:52














  • 1




    $begingroup$
    For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:43






  • 1




    $begingroup$
    For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
    $endgroup$
    – darij grinberg
    Dec 4 '18 at 0:44










  • $begingroup$
    Thanks for the replies! Very helpful.
    $endgroup$
    – Jeremiah Goertz
    Dec 5 '18 at 1:52








1




1




$begingroup$
For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
$endgroup$
– darij grinberg
Dec 4 '18 at 0:43




$begingroup$
For "similar", it is true and is a particular case of mathoverflow.net/questions/9162/… .
$endgroup$
– darij grinberg
Dec 4 '18 at 0:43




1




1




$begingroup$
For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
$endgroup$
– darij grinberg
Dec 4 '18 at 0:44




$begingroup$
For "equivalent" (I think the standard word for this is "congruent"), it is true because each matrix is equivalent to its rank normal form (and of course, the rank of a matrix does not change when we extend the field).
$endgroup$
– darij grinberg
Dec 4 '18 at 0:44












$begingroup$
Thanks for the replies! Very helpful.
$endgroup$
– Jeremiah Goertz
Dec 5 '18 at 1:52




$begingroup$
Thanks for the replies! Very helpful.
$endgroup$
– Jeremiah Goertz
Dec 5 '18 at 1:52










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