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?







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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?







    share|cite|improve this question





















      up vote
      0
      down vote

      favorite









      up vote
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      down vote

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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?







      share|cite|improve this question












      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?









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      share|cite|improve this question









      asked Jul 31 at 17:12









      philip

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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.






          share|cite|improve this answer





















          • 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










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          1 Answer
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          1 Answer
          1






          active

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          active

          oldest

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          active

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          up vote
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          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.






          share|cite|improve this answer





















          • 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














          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.






          share|cite|improve this answer





















          • 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












          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.






          share|cite|improve this answer













          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.







          share|cite|improve this answer













          share|cite|improve this answer



          share|cite|improve this answer











          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
















          • 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












           

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