Finding the matrix of $L$ with respect to the following bases:
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Let $L:mathbbR^3rightarrowmathbbR^4$ be the linear map:
$$L((x_1,x_2,x_3)^T)=(x_1-x_2+x_3,x_1-2x_2,x_2-3x_3,2x_1+x_3)^T$$
Find the matrix of $L$ with respect to the following bases: $(0,0,1)^T,(0,1,1)^T,(1,1,1)^T$ for$mathbbR^3$ and $(0,1,0,0)^T,(1,1,0,0)^T,(0,0,1,0)^T,(0,0,1,1)^T$ for $mathbbR^4$
My try:
Given $beginbmatrix x_1 \ x_2 \ x_3 endbmatrix=beginbmatrix x_1-x_2+x_3 \ x_1-2x_2 \ x_2-3x_3 \ 2x_1+x_3 endbmatrix=x_1beginbmatrix 1 \ 1 \ 0 \ 2 endbmatrix+x_2beginbmatrix -1 \ -2 \ 1 \ 0 endbmatrix+x_3beginbmatrix 1 \ 0 \ -3 \ 1 endbmatrix$
After this I have no idea what to do. Can anyone please explain how to proceed further?
linear-algebra
add a comment |Â
up vote
0
down vote
favorite
Let $L:mathbbR^3rightarrowmathbbR^4$ be the linear map:
$$L((x_1,x_2,x_3)^T)=(x_1-x_2+x_3,x_1-2x_2,x_2-3x_3,2x_1+x_3)^T$$
Find the matrix of $L$ with respect to the following bases: $(0,0,1)^T,(0,1,1)^T,(1,1,1)^T$ for$mathbbR^3$ and $(0,1,0,0)^T,(1,1,0,0)^T,(0,0,1,0)^T,(0,0,1,1)^T$ for $mathbbR^4$
My try:
Given $beginbmatrix x_1 \ x_2 \ x_3 endbmatrix=beginbmatrix x_1-x_2+x_3 \ x_1-2x_2 \ x_2-3x_3 \ 2x_1+x_3 endbmatrix=x_1beginbmatrix 1 \ 1 \ 0 \ 2 endbmatrix+x_2beginbmatrix -1 \ -2 \ 1 \ 0 endbmatrix+x_3beginbmatrix 1 \ 0 \ -3 \ 1 endbmatrix$
After this I have no idea what to do. Can anyone please explain how to proceed further?
linear-algebra
add a comment |Â
up vote
0
down vote
favorite
up vote
0
down vote
favorite
Let $L:mathbbR^3rightarrowmathbbR^4$ be the linear map:
$$L((x_1,x_2,x_3)^T)=(x_1-x_2+x_3,x_1-2x_2,x_2-3x_3,2x_1+x_3)^T$$
Find the matrix of $L$ with respect to the following bases: $(0,0,1)^T,(0,1,1)^T,(1,1,1)^T$ for$mathbbR^3$ and $(0,1,0,0)^T,(1,1,0,0)^T,(0,0,1,0)^T,(0,0,1,1)^T$ for $mathbbR^4$
My try:
Given $beginbmatrix x_1 \ x_2 \ x_3 endbmatrix=beginbmatrix x_1-x_2+x_3 \ x_1-2x_2 \ x_2-3x_3 \ 2x_1+x_3 endbmatrix=x_1beginbmatrix 1 \ 1 \ 0 \ 2 endbmatrix+x_2beginbmatrix -1 \ -2 \ 1 \ 0 endbmatrix+x_3beginbmatrix 1 \ 0 \ -3 \ 1 endbmatrix$
After this I have no idea what to do. Can anyone please explain how to proceed further?
linear-algebra
Let $L:mathbbR^3rightarrowmathbbR^4$ be the linear map:
$$L((x_1,x_2,x_3)^T)=(x_1-x_2+x_3,x_1-2x_2,x_2-3x_3,2x_1+x_3)^T$$
Find the matrix of $L$ with respect to the following bases: $(0,0,1)^T,(0,1,1)^T,(1,1,1)^T$ for$mathbbR^3$ and $(0,1,0,0)^T,(1,1,0,0)^T,(0,0,1,0)^T,(0,0,1,1)^T$ for $mathbbR^4$
My try:
Given $beginbmatrix x_1 \ x_2 \ x_3 endbmatrix=beginbmatrix x_1-x_2+x_3 \ x_1-2x_2 \ x_2-3x_3 \ 2x_1+x_3 endbmatrix=x_1beginbmatrix 1 \ 1 \ 0 \ 2 endbmatrix+x_2beginbmatrix -1 \ -2 \ 1 \ 0 endbmatrix+x_3beginbmatrix 1 \ 0 \ -3 \ 1 endbmatrix$
After this I have no idea what to do. Can anyone please explain how to proceed further?
linear-algebra
asked Jul 31 at 17:12
philip
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938
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1 Answer
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Let's give names to the bases-you have a basis $B=(e_1,e_2,e_3)$ in $mathbbR^3$ and a basis $C=(f_1,f_2,f_3,f_4)$ in $mathbbR^4$. By definition, the columns of the transformation matrix with respect to these bases are the coordinates of the vectors $L(e_1),L(e_2),L(e_3)$ with respect to the basis C. So calculate the vectors $L(e_1),L(e_2),L(e_3)$ and then calculate their coordinates in the basis C. That's simply solving systems of linear equations-might be annoying but not hard.
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
 |Â
show 4 more comments
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
Let's give names to the bases-you have a basis $B=(e_1,e_2,e_3)$ in $mathbbR^3$ and a basis $C=(f_1,f_2,f_3,f_4)$ in $mathbbR^4$. By definition, the columns of the transformation matrix with respect to these bases are the coordinates of the vectors $L(e_1),L(e_2),L(e_3)$ with respect to the basis C. So calculate the vectors $L(e_1),L(e_2),L(e_3)$ and then calculate their coordinates in the basis C. That's simply solving systems of linear equations-might be annoying but not hard.
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
 |Â
show 4 more comments
up vote
2
down vote
accepted
Let's give names to the bases-you have a basis $B=(e_1,e_2,e_3)$ in $mathbbR^3$ and a basis $C=(f_1,f_2,f_3,f_4)$ in $mathbbR^4$. By definition, the columns of the transformation matrix with respect to these bases are the coordinates of the vectors $L(e_1),L(e_2),L(e_3)$ with respect to the basis C. So calculate the vectors $L(e_1),L(e_2),L(e_3)$ and then calculate their coordinates in the basis C. That's simply solving systems of linear equations-might be annoying but not hard.
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
 |Â
show 4 more comments
up vote
2
down vote
accepted
up vote
2
down vote
accepted
Let's give names to the bases-you have a basis $B=(e_1,e_2,e_3)$ in $mathbbR^3$ and a basis $C=(f_1,f_2,f_3,f_4)$ in $mathbbR^4$. By definition, the columns of the transformation matrix with respect to these bases are the coordinates of the vectors $L(e_1),L(e_2),L(e_3)$ with respect to the basis C. So calculate the vectors $L(e_1),L(e_2),L(e_3)$ and then calculate their coordinates in the basis C. That's simply solving systems of linear equations-might be annoying but not hard.
Let's give names to the bases-you have a basis $B=(e_1,e_2,e_3)$ in $mathbbR^3$ and a basis $C=(f_1,f_2,f_3,f_4)$ in $mathbbR^4$. By definition, the columns of the transformation matrix with respect to these bases are the coordinates of the vectors $L(e_1),L(e_2),L(e_3)$ with respect to the basis C. So calculate the vectors $L(e_1),L(e_2),L(e_3)$ and then calculate their coordinates in the basis C. That's simply solving systems of linear equations-might be annoying but not hard.
answered Jul 31 at 17:22
Mark
5949
5949
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
 |Â
show 4 more comments
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
So, I just need to plug in $e_1,e_2,e_3$ in $L(x_1,x_2,x_3)^T$ right?
– philip
Jul 31 at 18:08
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
Yes, you need to use the transformation $L$ on each of the vectors $e_1,e_2,e_3$. In the basis you wrote you have $e_1=(0,0,1)$, $e_2=(0,1,1)$, $e_3=(1,1,1)$. And as I wrote, you then need to calculate the coordinates of the vectors you get with respect to the basis in $mathbbR^4$ that is given to you. (and not with respect to the standard basis of $mathbbR^4$)
– Mark
Jul 31 at 18:20
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
So, when I plugged in $e_1,e_2,e_3$ in $L$ I got the matrix as $beginbmatrix 1 & 0 & 1 \ 0 & -2 & -1 \ -3 & -2 & -2 \ 1 & 1 & 3 endbmatrix$ is it correct
– philip
Jul 31 at 19:15
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
And how should I plug in $f_1,f_2,f_3,f_4$ because there is no $x_4$ term in the given $L$
– philip
Jul 31 at 19:16
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
Ok, you calculated the vectors $L(e_1),L(e_2),L(e_3)$. Now you need to find their coordinates with respect to the basis $(f_1,f_2,f_3,f_4)$. Coordinates of $L(e_1)$ with respect to the basis are scalars $a,b,c,d$ such that $L(e_1)=af_1+bf_2+cf_3+df_4$. Find them and then $(a,b,c,d)^T$ will be the first column in your matrix. Then do the same for $L(e_2)$ and $L(e_3)$.
– Mark
Jul 31 at 19:53
 |Â
show 4 more comments
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