What is the procedure finding the Orthogonal Basis of a Quadratic Form?Graphing quadratic form, which eigenvalue should be chosen first?Zero as an Eigenvalue of stress tensorfind real numbers so that a specific linear isometry existscondition for a binary quadratic form to be positive at infinityWhat is wrong with my calculation of Jordan canonical form?Find a positive-definite scalar product for which $F:mathbbR^3to mathbbR^3$ is symmetricalConfusion about orthogonal basis of a quadratic form.If $ax^2_1+by^2_1+cz^2_1=ax^2_2+by^2_2+cz^2_2=ax^2_3+by^2_3+cz^2_3=d$ and $ax_2x_3+by_2y_3+cz_2z_3=ax_3x_1+by_3y_1+cz_3z_1=ax_1x_2+by_1y_2+cz_1z_2=f$,Find basis of fundamental subspaces with given eigenvalues and eigenvectorsShow that $P^TAP$ reduces to the diagonal matrix $lambda_idelta_ij$

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What is the procedure finding the Orthogonal Basis of a Quadratic Form?


Graphing quadratic form, which eigenvalue should be chosen first?Zero as an Eigenvalue of stress tensorfind real numbers so that a specific linear isometry existscondition for a binary quadratic form to be positive at infinityWhat is wrong with my calculation of Jordan canonical form?Find a positive-definite scalar product for which $F:mathbbR^3to mathbbR^3$ is symmetricalConfusion about orthogonal basis of a quadratic form.If $ax^2_1+by^2_1+cz^2_1=ax^2_2+by^2_2+cz^2_2=ax^2_3+by^2_3+cz^2_3=d$ and $ax_2x_3+by_2y_3+cz_2z_3=ax_3x_1+by_3y_1+cz_3z_1=ax_1x_2+by_1y_2+cz_1z_2=f$,Find basis of fundamental subspaces with given eigenvalues and eigenvectorsShow that $P^TAP$ reduces to the diagonal matrix $lambda_idelta_ij$













1












$begingroup$


We have the following quadratic form:



$$q := 6 x^2_1 + 3 x^2_2 + 3 x^2_3 - 4 x_1 x_2 + 4 x_1 x_3 - 2 x_2 x_3$$



whose eigenvalues are $lambda_1=lambda_2=2$ and $lambda_3=8$



I am not really sure how could we get the procedure to find the orthogonal basis for this form...
For now, I know two things:
1. The Orthogonal Basis of the quadratic form was assumed randomly
2. Somehow we used some sort of "Witchcraft" from the eigenvectors.



Which one is true










share|cite|improve this question









New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$











  • $begingroup$
    This might be helpful: batty.mullikin.org/quadratic.pdf
    $endgroup$
    – enedil
    Mar 10 at 21:29










  • $begingroup$
    Have you ever heard of the Gram-Schmidt process?
    $endgroup$
    – amd
    Mar 10 at 21:53










  • $begingroup$
    Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
    $endgroup$
    – Rodrigo de Azevedo
    Mar 10 at 22:28










  • $begingroup$
    After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
    $endgroup$
    – EternalKore
    yesterday
















1












$begingroup$


We have the following quadratic form:



$$q := 6 x^2_1 + 3 x^2_2 + 3 x^2_3 - 4 x_1 x_2 + 4 x_1 x_3 - 2 x_2 x_3$$



whose eigenvalues are $lambda_1=lambda_2=2$ and $lambda_3=8$



I am not really sure how could we get the procedure to find the orthogonal basis for this form...
For now, I know two things:
1. The Orthogonal Basis of the quadratic form was assumed randomly
2. Somehow we used some sort of "Witchcraft" from the eigenvectors.



Which one is true










share|cite|improve this question









New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$











  • $begingroup$
    This might be helpful: batty.mullikin.org/quadratic.pdf
    $endgroup$
    – enedil
    Mar 10 at 21:29










  • $begingroup$
    Have you ever heard of the Gram-Schmidt process?
    $endgroup$
    – amd
    Mar 10 at 21:53










  • $begingroup$
    Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
    $endgroup$
    – Rodrigo de Azevedo
    Mar 10 at 22:28










  • $begingroup$
    After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
    $endgroup$
    – EternalKore
    yesterday














1












1








1





$begingroup$


We have the following quadratic form:



$$q := 6 x^2_1 + 3 x^2_2 + 3 x^2_3 - 4 x_1 x_2 + 4 x_1 x_3 - 2 x_2 x_3$$



whose eigenvalues are $lambda_1=lambda_2=2$ and $lambda_3=8$



I am not really sure how could we get the procedure to find the orthogonal basis for this form...
For now, I know two things:
1. The Orthogonal Basis of the quadratic form was assumed randomly
2. Somehow we used some sort of "Witchcraft" from the eigenvectors.



Which one is true










share|cite|improve this question









New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




We have the following quadratic form:



$$q := 6 x^2_1 + 3 x^2_2 + 3 x^2_3 - 4 x_1 x_2 + 4 x_1 x_3 - 2 x_2 x_3$$



whose eigenvalues are $lambda_1=lambda_2=2$ and $lambda_3=8$



I am not really sure how could we get the procedure to find the orthogonal basis for this form...
For now, I know two things:
1. The Orthogonal Basis of the quadratic form was assumed randomly
2. Somehow we used some sort of "Witchcraft" from the eigenvectors.



Which one is true







linear-algebra quadratic-forms






share|cite|improve this question









New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question









New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|cite|improve this question




share|cite|improve this question








edited Mar 10 at 22:27









Rodrigo de Azevedo

13k41960




13k41960






New contributor




EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked Mar 10 at 21:02









EternalKoreEternalKore

61




61




New contributor




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New contributor





EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






EternalKore is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











  • $begingroup$
    This might be helpful: batty.mullikin.org/quadratic.pdf
    $endgroup$
    – enedil
    Mar 10 at 21:29










  • $begingroup$
    Have you ever heard of the Gram-Schmidt process?
    $endgroup$
    – amd
    Mar 10 at 21:53










  • $begingroup$
    Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
    $endgroup$
    – Rodrigo de Azevedo
    Mar 10 at 22:28










  • $begingroup$
    After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
    $endgroup$
    – EternalKore
    yesterday

















  • $begingroup$
    This might be helpful: batty.mullikin.org/quadratic.pdf
    $endgroup$
    – enedil
    Mar 10 at 21:29










  • $begingroup$
    Have you ever heard of the Gram-Schmidt process?
    $endgroup$
    – amd
    Mar 10 at 21:53










  • $begingroup$
    Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
    $endgroup$
    – Rodrigo de Azevedo
    Mar 10 at 22:28










  • $begingroup$
    After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
    $endgroup$
    – EternalKore
    yesterday
















$begingroup$
This might be helpful: batty.mullikin.org/quadratic.pdf
$endgroup$
– enedil
Mar 10 at 21:29




$begingroup$
This might be helpful: batty.mullikin.org/quadratic.pdf
$endgroup$
– enedil
Mar 10 at 21:29












$begingroup$
Have you ever heard of the Gram-Schmidt process?
$endgroup$
– amd
Mar 10 at 21:53




$begingroup$
Have you ever heard of the Gram-Schmidt process?
$endgroup$
– amd
Mar 10 at 21:53












$begingroup$
Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
$endgroup$
– Rodrigo de Azevedo
Mar 10 at 22:28




$begingroup$
Isn't a quadratic form a polynomial? How can it have eigenvalues? If you're referring to the symmetric matrix one can use to write the quadratic form, please mention it.
$endgroup$
– Rodrigo de Azevedo
Mar 10 at 22:28












$begingroup$
After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
$endgroup$
– EternalKore
yesterday





$begingroup$
After I read my notes, I realised that I have to use the Gram-Schmidt process Much obliged @amd
$endgroup$
– EternalKore
yesterday











1 Answer
1






active

oldest

votes


















0












$begingroup$

Not quite sure exactly what it is you’re asking here. There are a couple of ways that you can find an orthogonal eigenbasis.



One way is to go through the normal process of finding a basis for each eigenspace. The eigenspace of $2$ will be two-dimensional, so orthogonalize the basis that you found for it using the Gram-Schmidt process.



Alternatively, recall that the eigenspaces are pairwise orthogonal, so since the ambient space is three-dimensional, the eigenspace of $2$ must be the orthogonal complement of the eigenspace of $8$. Find an eigenvector for the latter, generate a vector that’s orthogonal to it (I hope you can do at least that), and then take the cross product of these two vectors to complete the basis.






share|cite|improve this answer









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    1 Answer
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    active

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    active

    oldest

    votes









    0












    $begingroup$

    Not quite sure exactly what it is you’re asking here. There are a couple of ways that you can find an orthogonal eigenbasis.



    One way is to go through the normal process of finding a basis for each eigenspace. The eigenspace of $2$ will be two-dimensional, so orthogonalize the basis that you found for it using the Gram-Schmidt process.



    Alternatively, recall that the eigenspaces are pairwise orthogonal, so since the ambient space is three-dimensional, the eigenspace of $2$ must be the orthogonal complement of the eigenspace of $8$. Find an eigenvector for the latter, generate a vector that’s orthogonal to it (I hope you can do at least that), and then take the cross product of these two vectors to complete the basis.






    share|cite|improve this answer









    $endgroup$

















      0












      $begingroup$

      Not quite sure exactly what it is you’re asking here. There are a couple of ways that you can find an orthogonal eigenbasis.



      One way is to go through the normal process of finding a basis for each eigenspace. The eigenspace of $2$ will be two-dimensional, so orthogonalize the basis that you found for it using the Gram-Schmidt process.



      Alternatively, recall that the eigenspaces are pairwise orthogonal, so since the ambient space is three-dimensional, the eigenspace of $2$ must be the orthogonal complement of the eigenspace of $8$. Find an eigenvector for the latter, generate a vector that’s orthogonal to it (I hope you can do at least that), and then take the cross product of these two vectors to complete the basis.






      share|cite|improve this answer









      $endgroup$















        0












        0








        0





        $begingroup$

        Not quite sure exactly what it is you’re asking here. There are a couple of ways that you can find an orthogonal eigenbasis.



        One way is to go through the normal process of finding a basis for each eigenspace. The eigenspace of $2$ will be two-dimensional, so orthogonalize the basis that you found for it using the Gram-Schmidt process.



        Alternatively, recall that the eigenspaces are pairwise orthogonal, so since the ambient space is three-dimensional, the eigenspace of $2$ must be the orthogonal complement of the eigenspace of $8$. Find an eigenvector for the latter, generate a vector that’s orthogonal to it (I hope you can do at least that), and then take the cross product of these two vectors to complete the basis.






        share|cite|improve this answer









        $endgroup$



        Not quite sure exactly what it is you’re asking here. There are a couple of ways that you can find an orthogonal eigenbasis.



        One way is to go through the normal process of finding a basis for each eigenspace. The eigenspace of $2$ will be two-dimensional, so orthogonalize the basis that you found for it using the Gram-Schmidt process.



        Alternatively, recall that the eigenspaces are pairwise orthogonal, so since the ambient space is three-dimensional, the eigenspace of $2$ must be the orthogonal complement of the eigenspace of $8$. Find an eigenvector for the latter, generate a vector that’s orthogonal to it (I hope you can do at least that), and then take the cross product of these two vectors to complete the basis.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Mar 10 at 21:58









        amdamd

        30.9k21051




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