Jacobi Identity of Commutator of Vector Fields
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I want to proof the Jacobi identity of Lie brackets of vectorfields on smooth manifolds.
Let $ X=sum xi^ifrac{partial}{partial x^i} $, $ Y=sum eta^ifrac{partial}{partial x^i} $ and $ Z=sum zeta^ifrac{partial}{partial x^i} $. We defined $[X,Y]=sum(X(eta^i)-Y(xi^i)) frac{partial}{partial x^i}$.
Show that $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]=0$.
I tried to find antisymmetric parts*, but i faild. My try was:
$[[X,Y],Z]=[sum_i (X(eta^i)-Y(xi^i)frac{partial}{partial x^i}$,Z]=
$sum_j(sum_i(X(eta^i)-Y(xi^i))frac{partial}{partial x^i}(zeta^j))-sum zeta^ifrac{partial}{partial x^i}(X(eta^j)-Y(xi^i))$
I didn't write the other two doublebrackets because it was just too much chaos.
Should i try to go one layer down (eg. with $X(f)(x)=df_x(X(x))$) or am i on the wrong way?
*(like it's done with the matrix commutator)
differential-geometry lie-groups smooth-manifolds vector-fields
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add a comment |
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I want to proof the Jacobi identity of Lie brackets of vectorfields on smooth manifolds.
Let $ X=sum xi^ifrac{partial}{partial x^i} $, $ Y=sum eta^ifrac{partial}{partial x^i} $ and $ Z=sum zeta^ifrac{partial}{partial x^i} $. We defined $[X,Y]=sum(X(eta^i)-Y(xi^i)) frac{partial}{partial x^i}$.
Show that $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]=0$.
I tried to find antisymmetric parts*, but i faild. My try was:
$[[X,Y],Z]=[sum_i (X(eta^i)-Y(xi^i)frac{partial}{partial x^i}$,Z]=
$sum_j(sum_i(X(eta^i)-Y(xi^i))frac{partial}{partial x^i}(zeta^j))-sum zeta^ifrac{partial}{partial x^i}(X(eta^j)-Y(xi^i))$
I didn't write the other two doublebrackets because it was just too much chaos.
Should i try to go one layer down (eg. with $X(f)(x)=df_x(X(x))$) or am i on the wrong way?
*(like it's done with the matrix commutator)
differential-geometry lie-groups smooth-manifolds vector-fields
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1
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Have you tried simplifying the associator?
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– J.G.
Jan 7 at 19:52
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Sorry, what do you mean by that?
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– Timmathstf
Jan 7 at 20:03
1
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@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
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– J.G.
Jan 7 at 20:06
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Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08
add a comment |
$begingroup$
I want to proof the Jacobi identity of Lie brackets of vectorfields on smooth manifolds.
Let $ X=sum xi^ifrac{partial}{partial x^i} $, $ Y=sum eta^ifrac{partial}{partial x^i} $ and $ Z=sum zeta^ifrac{partial}{partial x^i} $. We defined $[X,Y]=sum(X(eta^i)-Y(xi^i)) frac{partial}{partial x^i}$.
Show that $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]=0$.
I tried to find antisymmetric parts*, but i faild. My try was:
$[[X,Y],Z]=[sum_i (X(eta^i)-Y(xi^i)frac{partial}{partial x^i}$,Z]=
$sum_j(sum_i(X(eta^i)-Y(xi^i))frac{partial}{partial x^i}(zeta^j))-sum zeta^ifrac{partial}{partial x^i}(X(eta^j)-Y(xi^i))$
I didn't write the other two doublebrackets because it was just too much chaos.
Should i try to go one layer down (eg. with $X(f)(x)=df_x(X(x))$) or am i on the wrong way?
*(like it's done with the matrix commutator)
differential-geometry lie-groups smooth-manifolds vector-fields
$endgroup$
I want to proof the Jacobi identity of Lie brackets of vectorfields on smooth manifolds.
Let $ X=sum xi^ifrac{partial}{partial x^i} $, $ Y=sum eta^ifrac{partial}{partial x^i} $ and $ Z=sum zeta^ifrac{partial}{partial x^i} $. We defined $[X,Y]=sum(X(eta^i)-Y(xi^i)) frac{partial}{partial x^i}$.
Show that $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]=0$.
I tried to find antisymmetric parts*, but i faild. My try was:
$[[X,Y],Z]=[sum_i (X(eta^i)-Y(xi^i)frac{partial}{partial x^i}$,Z]=
$sum_j(sum_i(X(eta^i)-Y(xi^i))frac{partial}{partial x^i}(zeta^j))-sum zeta^ifrac{partial}{partial x^i}(X(eta^j)-Y(xi^i))$
I didn't write the other two doublebrackets because it was just too much chaos.
Should i try to go one layer down (eg. with $X(f)(x)=df_x(X(x))$) or am i on the wrong way?
*(like it's done with the matrix commutator)
differential-geometry lie-groups smooth-manifolds vector-fields
differential-geometry lie-groups smooth-manifolds vector-fields
edited Jan 7 at 19:21
Timmathstf
asked Jan 7 at 18:17
TimmathstfTimmathstf
307
307
1
$begingroup$
Have you tried simplifying the associator?
$endgroup$
– J.G.
Jan 7 at 19:52
$begingroup$
Sorry, what do you mean by that?
$endgroup$
– Timmathstf
Jan 7 at 20:03
1
$begingroup$
@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
$endgroup$
– J.G.
Jan 7 at 20:06
$begingroup$
Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08
add a comment |
1
$begingroup$
Have you tried simplifying the associator?
$endgroup$
– J.G.
Jan 7 at 19:52
$begingroup$
Sorry, what do you mean by that?
$endgroup$
– Timmathstf
Jan 7 at 20:03
1
$begingroup$
@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
$endgroup$
– J.G.
Jan 7 at 20:06
$begingroup$
Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08
1
1
$begingroup$
Have you tried simplifying the associator?
$endgroup$
– J.G.
Jan 7 at 19:52
$begingroup$
Have you tried simplifying the associator?
$endgroup$
– J.G.
Jan 7 at 19:52
$begingroup$
Sorry, what do you mean by that?
$endgroup$
– Timmathstf
Jan 7 at 20:03
$begingroup$
Sorry, what do you mean by that?
$endgroup$
– Timmathstf
Jan 7 at 20:03
1
1
$begingroup$
@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
$endgroup$
– J.G.
Jan 7 at 20:06
$begingroup$
@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
$endgroup$
– J.G.
Jan 7 at 20:06
$begingroup$
Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08
$begingroup$
Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08
add a comment |
1 Answer
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Ok, a buddy helped me out. Apperently it is easier to go a slightly different way.
The key in his solution is that $Xequiv 0 Leftrightarrow X(f)=0quadforall fin C^infty(M)$.
Note: $[X,Y](f)=X(Y(f))-Y(X(f))$
Now : $[[X,Y],Z]=X(Y(Z(f)))-Y(X(Z(f)))-Z(X(Y(f)))-Z(Y(X(f)))$
Notation $Z(Y(X(f)))=:ZYX$
And finaly $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]= XYZ-YXZ+ZYX-ZXY+YZX-XZY+YXZ-XYZ+ZXY-ZYX+XZY-YZX=0$
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add a comment |
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$begingroup$
Ok, a buddy helped me out. Apperently it is easier to go a slightly different way.
The key in his solution is that $Xequiv 0 Leftrightarrow X(f)=0quadforall fin C^infty(M)$.
Note: $[X,Y](f)=X(Y(f))-Y(X(f))$
Now : $[[X,Y],Z]=X(Y(Z(f)))-Y(X(Z(f)))-Z(X(Y(f)))-Z(Y(X(f)))$
Notation $Z(Y(X(f)))=:ZYX$
And finaly $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]= XYZ-YXZ+ZYX-ZXY+YZX-XZY+YXZ-XYZ+ZXY-ZYX+XZY-YZX=0$
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add a comment |
$begingroup$
Ok, a buddy helped me out. Apperently it is easier to go a slightly different way.
The key in his solution is that $Xequiv 0 Leftrightarrow X(f)=0quadforall fin C^infty(M)$.
Note: $[X,Y](f)=X(Y(f))-Y(X(f))$
Now : $[[X,Y],Z]=X(Y(Z(f)))-Y(X(Z(f)))-Z(X(Y(f)))-Z(Y(X(f)))$
Notation $Z(Y(X(f)))=:ZYX$
And finaly $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]= XYZ-YXZ+ZYX-ZXY+YZX-XZY+YXZ-XYZ+ZXY-ZYX+XZY-YZX=0$
$endgroup$
add a comment |
$begingroup$
Ok, a buddy helped me out. Apperently it is easier to go a slightly different way.
The key in his solution is that $Xequiv 0 Leftrightarrow X(f)=0quadforall fin C^infty(M)$.
Note: $[X,Y](f)=X(Y(f))-Y(X(f))$
Now : $[[X,Y],Z]=X(Y(Z(f)))-Y(X(Z(f)))-Z(X(Y(f)))-Z(Y(X(f)))$
Notation $Z(Y(X(f)))=:ZYX$
And finaly $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]= XYZ-YXZ+ZYX-ZXY+YZX-XZY+YXZ-XYZ+ZXY-ZYX+XZY-YZX=0$
$endgroup$
Ok, a buddy helped me out. Apperently it is easier to go a slightly different way.
The key in his solution is that $Xequiv 0 Leftrightarrow X(f)=0quadforall fin C^infty(M)$.
Note: $[X,Y](f)=X(Y(f))-Y(X(f))$
Now : $[[X,Y],Z]=X(Y(Z(f)))-Y(X(Z(f)))-Z(X(Y(f)))-Z(Y(X(f)))$
Notation $Z(Y(X(f)))=:ZYX$
And finaly $[[X,Y],Z]+[[Y,Z],X]+[[Z,X],Y]= XYZ-YXZ+ZYX-ZXY+YZX-XZY+YXZ-XYZ+ZXY-ZYX+XZY-YZX=0$
answered Jan 7 at 20:02
TimmathstfTimmathstf
307
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1
$begingroup$
Have you tried simplifying the associator?
$endgroup$
– J.G.
Jan 7 at 19:52
$begingroup$
Sorry, what do you mean by that?
$endgroup$
– Timmathstf
Jan 7 at 20:03
1
$begingroup$
@Timmathsf The associator quantifies how much associativity fails, just as the commutator quantifies how much commutativity fails. Ultimately, you used associativity to answer your own question.
$endgroup$
– J.G.
Jan 7 at 20:06
$begingroup$
Ah ok, thank you. I will add that to my vocabulary. :)
$endgroup$
– Timmathstf
Jan 7 at 20:08