Finding the matrix form of a linear operator with a non canonical vector space $V$?












0












$begingroup$


Given a vector space $V ={acos(t) + bsin(t) + ctsin(t)}$ with $a,b,c$ all real, a basis $B = {cos(t),sin(t),tsin(t)}$ and a Linear operator $Lf(t) = f''(t)$, how would I write ${lbrack Lrbrack}_{BB}$?



I attempted it and got begin{bmatrix}
-1 & 0 & 2t \
0 & -1 & 0 \
0 & 0 & -t
end{bmatrix}



however my professor shows the matrix representation as being



begin{bmatrix}
-1 & 0 & 2 \
0 & -1 & 0 \
0 & 0 & -1
end{bmatrix}



and so I am unsure as to why the $t$ disappeared










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$endgroup$








  • 1




    $begingroup$
    $L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
    $endgroup$
    – Mindlack
    Dec 13 '18 at 1:52












  • $begingroup$
    Well that's embarrassing, you're right, thanks
    $endgroup$
    – user3491700
    Dec 13 '18 at 2:00
















0












$begingroup$


Given a vector space $V ={acos(t) + bsin(t) + ctsin(t)}$ with $a,b,c$ all real, a basis $B = {cos(t),sin(t),tsin(t)}$ and a Linear operator $Lf(t) = f''(t)$, how would I write ${lbrack Lrbrack}_{BB}$?



I attempted it and got begin{bmatrix}
-1 & 0 & 2t \
0 & -1 & 0 \
0 & 0 & -t
end{bmatrix}



however my professor shows the matrix representation as being



begin{bmatrix}
-1 & 0 & 2 \
0 & -1 & 0 \
0 & 0 & -1
end{bmatrix}



and so I am unsure as to why the $t$ disappeared










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    $L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
    $endgroup$
    – Mindlack
    Dec 13 '18 at 1:52












  • $begingroup$
    Well that's embarrassing, you're right, thanks
    $endgroup$
    – user3491700
    Dec 13 '18 at 2:00














0












0








0





$begingroup$


Given a vector space $V ={acos(t) + bsin(t) + ctsin(t)}$ with $a,b,c$ all real, a basis $B = {cos(t),sin(t),tsin(t)}$ and a Linear operator $Lf(t) = f''(t)$, how would I write ${lbrack Lrbrack}_{BB}$?



I attempted it and got begin{bmatrix}
-1 & 0 & 2t \
0 & -1 & 0 \
0 & 0 & -t
end{bmatrix}



however my professor shows the matrix representation as being



begin{bmatrix}
-1 & 0 & 2 \
0 & -1 & 0 \
0 & 0 & -1
end{bmatrix}



and so I am unsure as to why the $t$ disappeared










share|cite|improve this question









$endgroup$




Given a vector space $V ={acos(t) + bsin(t) + ctsin(t)}$ with $a,b,c$ all real, a basis $B = {cos(t),sin(t),tsin(t)}$ and a Linear operator $Lf(t) = f''(t)$, how would I write ${lbrack Lrbrack}_{BB}$?



I attempted it and got begin{bmatrix}
-1 & 0 & 2t \
0 & -1 & 0 \
0 & 0 & -t
end{bmatrix}



however my professor shows the matrix representation as being



begin{bmatrix}
-1 & 0 & 2 \
0 & -1 & 0 \
0 & 0 & -1
end{bmatrix}



and so I am unsure as to why the $t$ disappeared







linear-algebra matrices linear-transformations






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share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 13 '18 at 1:47









user3491700user3491700

535




535








  • 1




    $begingroup$
    $L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
    $endgroup$
    – Mindlack
    Dec 13 '18 at 1:52












  • $begingroup$
    Well that's embarrassing, you're right, thanks
    $endgroup$
    – user3491700
    Dec 13 '18 at 2:00














  • 1




    $begingroup$
    $L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
    $endgroup$
    – Mindlack
    Dec 13 '18 at 1:52












  • $begingroup$
    Well that's embarrassing, you're right, thanks
    $endgroup$
    – user3491700
    Dec 13 '18 at 2:00








1




1




$begingroup$
$L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
$endgroup$
– Mindlack
Dec 13 '18 at 1:52






$begingroup$
$L(tsin(t))=(tcos(t)+sin(t))’=tsin(t)+2cos(t)$. So L(third vector of B) is 2[first vector of B]+(-1)[last vector of B]
$endgroup$
– Mindlack
Dec 13 '18 at 1:52














$begingroup$
Well that's embarrassing, you're right, thanks
$endgroup$
– user3491700
Dec 13 '18 at 2:00




$begingroup$
Well that's embarrassing, you're right, thanks
$endgroup$
– user3491700
Dec 13 '18 at 2:00










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