Principal axis of a matrix

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I try to find the definition of the main axis of a matrix.
I saw this phrase in some exercise:




Let $A$ be a positive matrix, $f:Glongrightarrow mathbbR$ a smooth function, $G$ an open set in $mathbbR^n$. I need to find the orthogonal coordinate transformation $y=Px$ such that the main axis on $y$'s coordinates will be the principle axis of $A$.




The book says to diagonalize $A$: $PAP^t=D$ and to choose $P$ to be the transformation.



What is the definition of principle axis of matrix?
thanks.







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  • the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
    – abel
    May 29 '15 at 16:13






  • 1




    I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
    – Ted Shifrin
    Jan 31 at 23:18














up vote
0
down vote

favorite












I try to find the definition of the main axis of a matrix.
I saw this phrase in some exercise:




Let $A$ be a positive matrix, $f:Glongrightarrow mathbbR$ a smooth function, $G$ an open set in $mathbbR^n$. I need to find the orthogonal coordinate transformation $y=Px$ such that the main axis on $y$'s coordinates will be the principle axis of $A$.




The book says to diagonalize $A$: $PAP^t=D$ and to choose $P$ to be the transformation.



What is the definition of principle axis of matrix?
thanks.







share|cite|improve this question






















  • the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
    – abel
    May 29 '15 at 16:13






  • 1




    I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
    – Ted Shifrin
    Jan 31 at 23:18












up vote
0
down vote

favorite









up vote
0
down vote

favorite











I try to find the definition of the main axis of a matrix.
I saw this phrase in some exercise:




Let $A$ be a positive matrix, $f:Glongrightarrow mathbbR$ a smooth function, $G$ an open set in $mathbbR^n$. I need to find the orthogonal coordinate transformation $y=Px$ such that the main axis on $y$'s coordinates will be the principle axis of $A$.




The book says to diagonalize $A$: $PAP^t=D$ and to choose $P$ to be the transformation.



What is the definition of principle axis of matrix?
thanks.







share|cite|improve this question














I try to find the definition of the main axis of a matrix.
I saw this phrase in some exercise:




Let $A$ be a positive matrix, $f:Glongrightarrow mathbbR$ a smooth function, $G$ an open set in $mathbbR^n$. I need to find the orthogonal coordinate transformation $y=Px$ such that the main axis on $y$'s coordinates will be the principle axis of $A$.




The book says to diagonalize $A$: $PAP^t=D$ and to choose $P$ to be the transformation.



What is the definition of principle axis of matrix?
thanks.









share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited May 29 '15 at 16:11









abel

26.3k11947




26.3k11947










asked Apr 9 '13 at 20:59









user56714

25119




25119











  • the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
    – abel
    May 29 '15 at 16:13






  • 1




    I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
    – Ted Shifrin
    Jan 31 at 23:18
















  • the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
    – abel
    May 29 '15 at 16:13






  • 1




    I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
    – Ted Shifrin
    Jan 31 at 23:18















the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
– abel
May 29 '15 at 16:13




the principal axis of a matrix $A$ are the basis vectors so that $A$ has a diagonal matrix representation.
– abel
May 29 '15 at 16:13




1




1




I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
– Ted Shifrin
Jan 31 at 23:18




I'm troubled by the "the" in this statement. Is this an English translation issue? Do we mean a principal [NOT principle] axis?
– Ted Shifrin
Jan 31 at 23:18










1 Answer
1






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Often, principal axes of a matrix refer to its eigenvectors. With this diagonalization, $P$ is the matrix of eigenvectors.






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  • when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
    – user56714
    Apr 9 '13 at 21:17






  • 1




    actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
    – Quang Hoang
    Sep 10 '15 at 11:09










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1 Answer
1






active

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1 Answer
1






active

oldest

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active

oldest

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active

oldest

votes








up vote
0
down vote













Often, principal axes of a matrix refer to its eigenvectors. With this diagonalization, $P$ is the matrix of eigenvectors.






share|cite|improve this answer




















  • when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
    – user56714
    Apr 9 '13 at 21:17






  • 1




    actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
    – Quang Hoang
    Sep 10 '15 at 11:09














up vote
0
down vote













Often, principal axes of a matrix refer to its eigenvectors. With this diagonalization, $P$ is the matrix of eigenvectors.






share|cite|improve this answer




















  • when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
    – user56714
    Apr 9 '13 at 21:17






  • 1




    actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
    – Quang Hoang
    Sep 10 '15 at 11:09












up vote
0
down vote










up vote
0
down vote









Often, principal axes of a matrix refer to its eigenvectors. With this diagonalization, $P$ is the matrix of eigenvectors.






share|cite|improve this answer












Often, principal axes of a matrix refer to its eigenvectors. With this diagonalization, $P$ is the matrix of eigenvectors.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Apr 9 '13 at 21:01









Ross B.

1,587516




1,587516











  • when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
    – user56714
    Apr 9 '13 at 21:17






  • 1




    actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
    – Quang Hoang
    Sep 10 '15 at 11:09
















  • when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
    – user56714
    Apr 9 '13 at 21:17






  • 1




    actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
    – Quang Hoang
    Sep 10 '15 at 11:09















when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
– user56714
Apr 9 '13 at 21:17




when you diagnolize matrix with orthogonal matrix p,p doesn't have to contain eigenvectors(grahm schmidt process might change them)
– user56714
Apr 9 '13 at 21:17




1




1




actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
– Quang Hoang
Sep 10 '15 at 11:09




actually, you can only diagonalize $A$ using orthogonal matrix $P$ when $A$ is symmetric (why?). It follows that $P$ is always composed of eigenvector columns.
– Quang Hoang
Sep 10 '15 at 11:09












 

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