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Calculating Exterior Derivative in Diffe...

Rakshak 80 Maple
grtensorii differentialgeometry tensor
May 24 2022
1 1

I am having trouble calculating exterior derivatives for one forms, maple does not seem to recognize them as one forms.

 
> 

Delta := -2*M*R+R^2+a^2
> 

Sigma2 := (R^2+a^2)^2-Delta*a^2*sin(Theta)^2
> 

rho2 := R^2+a^2*cos(Theta)^2
> 

z := 2*M*R/rho2
> 

interface(typesetting = extended)
> 

with(DifferentialGeometry); with(Tensor)
> 

DGsetup([T, R, Theta, Phi], BlackHole, verbose)

`The following coordinates have been protected:`

  

[T, R, Theta, Phi]

  

`The following vector fields have been defined and protected:`

  

[_DG([["vector", BlackHole, []], [[[1], 1]]]), _DG([["vector", BlackHole, []], [[[2], 1]]]), _DG([["vector", BlackHole, []], [[[3], 1]]]), _DG([["vector", BlackHole, []], [[[4], 1]]])]

  

`The following differential 1-forms have been defined and protected:`

  

[_DG([["form", BlackHole, 1], [[[1], 1]]]), _DG([["form", BlackHole, 1], [[[2], 1]]]), _DG([["form", BlackHole, 1], [[[3], 1]]]), _DG([["form", BlackHole, 1], [[[4], 1]]])]

 (1)
BlackHole > 

g := evalDG((-1+z)*`&t`(dT, dT)+`&t`(dT, dR)+`&t`(dR, dT)+rho2*`&t`(dTheta, dTheta)-z*a*sin(Theta)^2*(`&t`(dPhi, dT)+`&t`(dT, dPhi))-a*sin(Theta)^2*(`&t`(dR, dPhi)+`&t`(dPhi, dR))+Sigma2*sin(Theta)^2*`&t`(dPhi, dPhi)/rho2)
BlackHole > 

ON := evalDG(DGGramSchmidt([D_T, D_R, D_Theta, D_Phi], g, signature = [-1, 1, 1, 1]))

[_DG([["vector", BlackHole, []], [[[1], 1/(-(-a^2*cos(Theta)^2+2*M*R-R^2)/(R^2+a^2*cos(Theta)^2))^(1/2)]]]), _DG([["vector", BlackHole, []], [[[1], -(R^2+a^2*cos(Theta)^2)/((-(R^2+a^2*cos(Theta)^2)/(-a^2*cos(Theta)^2+2*M*R-R^2))^(1/2)*(-a^2*cos(Theta)^2+2*M*R-R^2))], [[2], 1/(-(R^2+a^2*cos(Theta)^2)/(-a^2*cos(Theta)^2+2*M*R-R^2))^(1/2)]]]), _DG([["vector", BlackHole, []], [[[3], 1/(R^2+a^2*cos(Theta)^2)^(1/2)]]]), _DG([["vector", BlackHole, []], [[[1], a*sin(Theta)^2/((R^2+a^2*cos(Theta)^2)*sin(Theta)^2)^(1/2)], [[2], a*sin(Theta)^2/((R^2+a^2*cos(Theta)^2)*sin(Theta)^2)^(1/2)], [[4], 1/((R^2+a^2*cos(Theta)^2)*sin(Theta)^2)^(1/2)]]])]

 (2)
BlackHole > 

Oneform := RaiseLowerIndices(g, ON[1], [1])

_DG([["tensor", BlackHole, [["cov_bas"], []]], [[[1], (-a^2*cos(Theta)^2+2*M*R-R^2)/((R^2+a^2*cos(Theta)^2)*(-(-a^2*cos(Theta)^2+2*M*R-R^2)/(R^2+a^2*cos(Theta)^2))^(1/2))], [[2], 1/(-(-a^2*cos(Theta)^2+2*M*R-R^2)/(R^2+a^2*cos(Theta)^2))^(1/2)], [[4], -2*M*R*a*sin(Theta)^2/((R^2+a^2*cos(Theta)^2)*(-(-a^2*cos(Theta)^2+2*M*R-R^2)/(R^2+a^2*cos(Theta)^2))^(1/2))]]])

 (3)
BlackHole > 

ExteriorDerivative(Oneform)

Error, (in DifferentialGeometry:-ExteriorDerivative) expected 1st argument to be a differential form. Received: _DG([["tensor", BlackHole, [["cov_bas"], []]], [`...`]])

  
BlackHole > 

``

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