basis of a subspace that generates all of $Bbb R^3$











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I have a set of all $3times3$ matrices $B$ that have rank $0, 1$ or $2$ - what is the basis of a subspace that this set generates?



I came to the conclusion that this subspace consists of lines, planes and the null vector and it generates the whole space of $Bbb R^3$, but I don't know what is the basis of this subspace - is it just the set of all the $B$'s?










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  • Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
    – José Carlos Santos
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up vote
0
down vote

favorite












I have a set of all $3times3$ matrices $B$ that have rank $0, 1$ or $2$ - what is the basis of a subspace that this set generates?



I came to the conclusion that this subspace consists of lines, planes and the null vector and it generates the whole space of $Bbb R^3$, but I don't know what is the basis of this subspace - is it just the set of all the $B$'s?










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  • Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
    – José Carlos Santos
    22 hours ago













up vote
0
down vote

favorite









up vote
0
down vote

favorite











I have a set of all $3times3$ matrices $B$ that have rank $0, 1$ or $2$ - what is the basis of a subspace that this set generates?



I came to the conclusion that this subspace consists of lines, planes and the null vector and it generates the whole space of $Bbb R^3$, but I don't know what is the basis of this subspace - is it just the set of all the $B$'s?










share|cite|improve this question









New contributor




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











I have a set of all $3times3$ matrices $B$ that have rank $0, 1$ or $2$ - what is the basis of a subspace that this set generates?



I came to the conclusion that this subspace consists of lines, planes and the null vector and it generates the whole space of $Bbb R^3$, but I don't know what is the basis of this subspace - is it just the set of all the $B$'s?







linear-algebra matrices matrix-rank






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edited 22 hours ago









Tianlalu

2,559632




2,559632






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asked 22 hours ago









agromek

1




1




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  • Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
    – José Carlos Santos
    22 hours ago


















  • Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
    – José Carlos Santos
    22 hours ago
















Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
22 hours ago




Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
22 hours ago










2 Answers
2






active

oldest

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up vote
0
down vote













It's unclear which space you're talking about---subspace of what? If you are viewing $3times3$ matrices as elements of $V=mathbb R^{3,3}$ i.e. $3times3$ matrices under addition, then the answer is all of $V$.






share|cite|improve this answer





















  • the set of B matrices is the subspace of R^3
    – agromek
    22 hours ago










  • No, I don't think so.
    – Richard Martin
    22 hours ago










  • the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
    – agromek
    22 hours ago












  • maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
    – agromek
    22 hours ago










  • The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
    – Richard Martin
    22 hours ago


















up vote
0
down vote













The vector space of all $3 x 3$ matrices is not $R^3$. You can verify that the space has dimension $9$ because you will need $9$ vectors for a basis. Probably the most likely ones would be $begin{bmatrix}1 & 0 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 1 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$ ... $begin{bmatrix}0 & 0 & 1\0 & 0 & 0\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\1 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 1 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 1\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\0 & 0 & 0\1 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 1 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 0 & 1end{bmatrix}$



Now considering that your subspace only contains matrices with rank $leq2$ the basis for that space will contain only $6$ of these $9$.






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Chai is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • SInce all those matrices have rank $le2$, they all belong to the given set.
    – egreg
    20 hours ago










  • Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
    – Chai
    20 hours ago










  • Well, every matrix belongs to the span of the rank $1$ matrices.
    – egreg
    20 hours ago










  • I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
    – Chai
    20 hours ago










  • I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
    – agromek
    16 hours ago











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2 Answers
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2 Answers
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active

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active

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active

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votes








up vote
0
down vote













It's unclear which space you're talking about---subspace of what? If you are viewing $3times3$ matrices as elements of $V=mathbb R^{3,3}$ i.e. $3times3$ matrices under addition, then the answer is all of $V$.






share|cite|improve this answer





















  • the set of B matrices is the subspace of R^3
    – agromek
    22 hours ago










  • No, I don't think so.
    – Richard Martin
    22 hours ago










  • the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
    – agromek
    22 hours ago












  • maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
    – agromek
    22 hours ago










  • The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
    – Richard Martin
    22 hours ago















up vote
0
down vote













It's unclear which space you're talking about---subspace of what? If you are viewing $3times3$ matrices as elements of $V=mathbb R^{3,3}$ i.e. $3times3$ matrices under addition, then the answer is all of $V$.






share|cite|improve this answer





















  • the set of B matrices is the subspace of R^3
    – agromek
    22 hours ago










  • No, I don't think so.
    – Richard Martin
    22 hours ago










  • the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
    – agromek
    22 hours ago












  • maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
    – agromek
    22 hours ago










  • The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
    – Richard Martin
    22 hours ago













up vote
0
down vote










up vote
0
down vote









It's unclear which space you're talking about---subspace of what? If you are viewing $3times3$ matrices as elements of $V=mathbb R^{3,3}$ i.e. $3times3$ matrices under addition, then the answer is all of $V$.






share|cite|improve this answer












It's unclear which space you're talking about---subspace of what? If you are viewing $3times3$ matrices as elements of $V=mathbb R^{3,3}$ i.e. $3times3$ matrices under addition, then the answer is all of $V$.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered 22 hours ago









Richard Martin

1,2588




1,2588












  • the set of B matrices is the subspace of R^3
    – agromek
    22 hours ago










  • No, I don't think so.
    – Richard Martin
    22 hours ago










  • the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
    – agromek
    22 hours ago












  • maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
    – agromek
    22 hours ago










  • The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
    – Richard Martin
    22 hours ago


















  • the set of B matrices is the subspace of R^3
    – agromek
    22 hours ago










  • No, I don't think so.
    – Richard Martin
    22 hours ago










  • the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
    – agromek
    22 hours ago












  • maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
    – agromek
    22 hours ago










  • The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
    – Richard Martin
    22 hours ago
















the set of B matrices is the subspace of R^3
– agromek
22 hours ago




the set of B matrices is the subspace of R^3
– agromek
22 hours ago












No, I don't think so.
– Richard Martin
22 hours ago




No, I don't think so.
– Richard Martin
22 hours ago












the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
– agromek
22 hours ago






the whole task was that I have two 3x3 matrices: A and C - A has rank 2 and C can be any 3x3 matrix and the question is: what is the basis of a subspace of the space of all 3x3 matrices that is generated by the set of 3x3 matrices B that satisfy the equation A*C=B (I'm trying to translate it into english as exact as I can)
– agromek
22 hours ago














maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
– agromek
22 hours ago




maybe I'm interpreting the phrase "the space of all 3x3 matrices" wrongly, I thought it is just R^3 but maybe it's something else?
– agromek
22 hours ago












The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
– Richard Martin
22 hours ago




The space of all 3x3 matrices acts on $mathbb R^3$ but it is not of itself $mathbb R^3$.
– Richard Martin
22 hours ago










up vote
0
down vote













The vector space of all $3 x 3$ matrices is not $R^3$. You can verify that the space has dimension $9$ because you will need $9$ vectors for a basis. Probably the most likely ones would be $begin{bmatrix}1 & 0 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 1 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$ ... $begin{bmatrix}0 & 0 & 1\0 & 0 & 0\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\1 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 1 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 1\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\0 & 0 & 0\1 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 1 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 0 & 1end{bmatrix}$



Now considering that your subspace only contains matrices with rank $leq2$ the basis for that space will contain only $6$ of these $9$.






share|cite|improve this answer










New contributor




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


















  • SInce all those matrices have rank $le2$, they all belong to the given set.
    – egreg
    20 hours ago










  • Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
    – Chai
    20 hours ago










  • Well, every matrix belongs to the span of the rank $1$ matrices.
    – egreg
    20 hours ago










  • I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
    – Chai
    20 hours ago










  • I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
    – agromek
    16 hours ago















up vote
0
down vote













The vector space of all $3 x 3$ matrices is not $R^3$. You can verify that the space has dimension $9$ because you will need $9$ vectors for a basis. Probably the most likely ones would be $begin{bmatrix}1 & 0 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 1 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$ ... $begin{bmatrix}0 & 0 & 1\0 & 0 & 0\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\1 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 1 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 1\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\0 & 0 & 0\1 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 1 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 0 & 1end{bmatrix}$



Now considering that your subspace only contains matrices with rank $leq2$ the basis for that space will contain only $6$ of these $9$.






share|cite|improve this answer










New contributor




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


















  • SInce all those matrices have rank $le2$, they all belong to the given set.
    – egreg
    20 hours ago










  • Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
    – Chai
    20 hours ago










  • Well, every matrix belongs to the span of the rank $1$ matrices.
    – egreg
    20 hours ago










  • I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
    – Chai
    20 hours ago










  • I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
    – agromek
    16 hours ago













up vote
0
down vote










up vote
0
down vote









The vector space of all $3 x 3$ matrices is not $R^3$. You can verify that the space has dimension $9$ because you will need $9$ vectors for a basis. Probably the most likely ones would be $begin{bmatrix}1 & 0 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 1 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$ ... $begin{bmatrix}0 & 0 & 1\0 & 0 & 0\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\1 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 1 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 1\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\0 & 0 & 0\1 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 1 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 0 & 1end{bmatrix}$



Now considering that your subspace only contains matrices with rank $leq2$ the basis for that space will contain only $6$ of these $9$.






share|cite|improve this answer










New contributor




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









The vector space of all $3 x 3$ matrices is not $R^3$. You can verify that the space has dimension $9$ because you will need $9$ vectors for a basis. Probably the most likely ones would be $begin{bmatrix}1 & 0 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 1 & 0\0 & 0 & 0\0 & 0 & 0end{bmatrix}$ ... $begin{bmatrix}0 & 0 & 1\0 & 0 & 0\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\1 & 0 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 1 & 0\0 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 1\0 & 0 & 0end{bmatrix}$,$begin{bmatrix}0 & 0 & 0\0 & 0 & 0\1 & 0 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 1 & 0end{bmatrix}$, $begin{bmatrix}0 & 0 & 0\0 & 0 & 0\0 & 0 & 1end{bmatrix}$



Now considering that your subspace only contains matrices with rank $leq2$ the basis for that space will contain only $6$ of these $9$.







share|cite|improve this answer










New contributor




Chai 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 answer



share|cite|improve this answer








edited 13 hours ago





















New contributor




Chai is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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answered 20 hours ago









Chai

1012




1012




New contributor




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





New contributor





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






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












  • SInce all those matrices have rank $le2$, they all belong to the given set.
    – egreg
    20 hours ago










  • Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
    – Chai
    20 hours ago










  • Well, every matrix belongs to the span of the rank $1$ matrices.
    – egreg
    20 hours ago










  • I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
    – Chai
    20 hours ago










  • I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
    – agromek
    16 hours ago


















  • SInce all those matrices have rank $le2$, they all belong to the given set.
    – egreg
    20 hours ago










  • Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
    – Chai
    20 hours ago










  • Well, every matrix belongs to the span of the rank $1$ matrices.
    – egreg
    20 hours ago










  • I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
    – Chai
    20 hours ago










  • I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
    – agromek
    16 hours ago
















SInce all those matrices have rank $le2$, they all belong to the given set.
– egreg
20 hours ago




SInce all those matrices have rank $le2$, they all belong to the given set.
– egreg
20 hours ago












Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
– Chai
20 hours ago




Is that true? Taking linear combinations of all $9$ will yield all possible matrices, including rank $3$ ones. If we leave out the ones that have 1's in the last column ofr instance, all combinations will have rank $leq2$ , or am I missing something?
– Chai
20 hours ago












Well, every matrix belongs to the span of the rank $1$ matrices.
– egreg
20 hours ago




Well, every matrix belongs to the span of the rank $1$ matrices.
– egreg
20 hours ago












I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
– Chai
20 hours ago




I'm not quite sure what you mean by that. As I understand it, OP is looking for a basis of the subspace of $3x3$ matrices that do not include the ones with rank$3$. I believe you could find a basis in this manner. But if I am wrong I'd like to learn as well !
– Chai
20 hours ago












I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
– agromek
16 hours ago




I don't really understand why the vector space of all 3x3 matrices has dimension 9? can someone please explain?
– agromek
16 hours ago










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