For row reduced echelon matrix for a homogeneous system of equations, what solution would be there for r=n...












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I was learning Linear Algebra from Hoffman and Kunze. There the authors prove that for a row reduced echelon matrix with rows r and columns n for a homogeneous system of equations X, if r < n, X has a non-trivial solution, which I understood (substituting, r unknowns with remaining unknowns). However, what would happen in case of




  1. r = n

  2. r > n


For r = n, I am guessing it would be trivial solution only as no substitution is possible. Please correct me if wrong.










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  • $begingroup$
    Well, just think how many unknowns are remaining to "substitute"?
    $endgroup$
    – Aniruddha Deshmukh
    Dec 28 '18 at 6:10










  • $begingroup$
    What is rank of the matrix?Is it r or less than than r?
    $endgroup$
    – ASHWINI SANKHE
    Dec 28 '18 at 6:59










  • $begingroup$
    @ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:28










  • $begingroup$
    @AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:54
















0












$begingroup$


I was learning Linear Algebra from Hoffman and Kunze. There the authors prove that for a row reduced echelon matrix with rows r and columns n for a homogeneous system of equations X, if r < n, X has a non-trivial solution, which I understood (substituting, r unknowns with remaining unknowns). However, what would happen in case of




  1. r = n

  2. r > n


For r = n, I am guessing it would be trivial solution only as no substitution is possible. Please correct me if wrong.










share|cite|improve this question









$endgroup$












  • $begingroup$
    Well, just think how many unknowns are remaining to "substitute"?
    $endgroup$
    – Aniruddha Deshmukh
    Dec 28 '18 at 6:10










  • $begingroup$
    What is rank of the matrix?Is it r or less than than r?
    $endgroup$
    – ASHWINI SANKHE
    Dec 28 '18 at 6:59










  • $begingroup$
    @ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:28










  • $begingroup$
    @AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:54














0












0








0





$begingroup$


I was learning Linear Algebra from Hoffman and Kunze. There the authors prove that for a row reduced echelon matrix with rows r and columns n for a homogeneous system of equations X, if r < n, X has a non-trivial solution, which I understood (substituting, r unknowns with remaining unknowns). However, what would happen in case of




  1. r = n

  2. r > n


For r = n, I am guessing it would be trivial solution only as no substitution is possible. Please correct me if wrong.










share|cite|improve this question









$endgroup$




I was learning Linear Algebra from Hoffman and Kunze. There the authors prove that for a row reduced echelon matrix with rows r and columns n for a homogeneous system of equations X, if r < n, X has a non-trivial solution, which I understood (substituting, r unknowns with remaining unknowns). However, what would happen in case of




  1. r = n

  2. r > n


For r = n, I am guessing it would be trivial solution only as no substitution is possible. Please correct me if wrong.







linear-algebra matrices homogeneous-equation






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asked Dec 28 '18 at 6:06









dheeraj suthardheeraj suthar

72




72












  • $begingroup$
    Well, just think how many unknowns are remaining to "substitute"?
    $endgroup$
    – Aniruddha Deshmukh
    Dec 28 '18 at 6:10










  • $begingroup$
    What is rank of the matrix?Is it r or less than than r?
    $endgroup$
    – ASHWINI SANKHE
    Dec 28 '18 at 6:59










  • $begingroup$
    @ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:28










  • $begingroup$
    @AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:54


















  • $begingroup$
    Well, just think how many unknowns are remaining to "substitute"?
    $endgroup$
    – Aniruddha Deshmukh
    Dec 28 '18 at 6:10










  • $begingroup$
    What is rank of the matrix?Is it r or less than than r?
    $endgroup$
    – ASHWINI SANKHE
    Dec 28 '18 at 6:59










  • $begingroup$
    @ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:28










  • $begingroup$
    @AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 7:54
















$begingroup$
Well, just think how many unknowns are remaining to "substitute"?
$endgroup$
– Aniruddha Deshmukh
Dec 28 '18 at 6:10




$begingroup$
Well, just think how many unknowns are remaining to "substitute"?
$endgroup$
– Aniruddha Deshmukh
Dec 28 '18 at 6:10












$begingroup$
What is rank of the matrix?Is it r or less than than r?
$endgroup$
– ASHWINI SANKHE
Dec 28 '18 at 6:59




$begingroup$
What is rank of the matrix?Is it r or less than than r?
$endgroup$
– ASHWINI SANKHE
Dec 28 '18 at 6:59












$begingroup$
@ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
$endgroup$
– dheeraj suthar
Dec 28 '18 at 7:28




$begingroup$
@ASHWINISANKHE It's r. I can't seem to correct my question. It should be like : reduced echelon matrix with with non-zero rows r. Sorry for the omission.
$endgroup$
– dheeraj suthar
Dec 28 '18 at 7:28












$begingroup$
@AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
$endgroup$
– dheeraj suthar
Dec 28 '18 at 7:54




$begingroup$
@AniruddhaDeshmukh I believe it should be zero for both case 1. and 2. So I think trivial solutions in case 2 also.
$endgroup$
– dheeraj suthar
Dec 28 '18 at 7:54










1 Answer
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$begingroup$

$Ax=0$ is homogeneous system.It always have trivial solution.If r=n then system will have trivial solution.As $rank(A)le min{(r,n)}$. Hence r can not be greater than n.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 8:55













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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









1












$begingroup$

$Ax=0$ is homogeneous system.It always have trivial solution.If r=n then system will have trivial solution.As $rank(A)le min{(r,n)}$. Hence r can not be greater than n.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 8:55


















1












$begingroup$

$Ax=0$ is homogeneous system.It always have trivial solution.If r=n then system will have trivial solution.As $rank(A)le min{(r,n)}$. Hence r can not be greater than n.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 8:55
















1












1








1





$begingroup$

$Ax=0$ is homogeneous system.It always have trivial solution.If r=n then system will have trivial solution.As $rank(A)le min{(r,n)}$. Hence r can not be greater than n.






share|cite|improve this answer









$endgroup$



$Ax=0$ is homogeneous system.It always have trivial solution.If r=n then system will have trivial solution.As $rank(A)le min{(r,n)}$. Hence r can not be greater than n.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Dec 28 '18 at 7:58









ASHWINI SANKHEASHWINI SANKHE

12710




12710












  • $begingroup$
    Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 8:55




















  • $begingroup$
    Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
    $endgroup$
    – dheeraj suthar
    Dec 28 '18 at 8:55


















$begingroup$
Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
$endgroup$
– dheeraj suthar
Dec 28 '18 at 8:55






$begingroup$
Thanks. I have not yet formally gone through the rank concept. But a quick search showed your assumption is true ( rank(A)≤min(r,n) ) . So both case 1 and 2 would have only trivial solutions. I guess I would have much better understanding once I go through the proof for rank(A)≤min(r,n)
$endgroup$
– dheeraj suthar
Dec 28 '18 at 8:55




















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