Question: Order of coefficients and brackets in metric


I was starting to set up a curved axisymmetric metric using the Physics package and came across an error message that I could not resolve. I was actually writing the metric in the form given after output line (5) in the code attcahed below. This returned the error message:

Error, (in Physics:-Setup) invalid subscript selector

Then I started fiddling and discovered that somehow braces and order of coefficients are making a difference in the metric. I have written the flat space metric in three different ways after output line (2). The difference is only in the coefficient of the last $d\phi^2$ term. For some reason, $r^2 (sin(\theta))^2$ is shown as $r (sin(\theta))^4$ in output line (3). Removing the brackets around $sin(theta)$ or writing $r^2$ after it is resolving the problem. Is this in someway related to the whole square operation? Can you please help me understand why this is happening?

The original error message I was getting went away after I similarly changed the order of coefficients in the second term of the curved metric to get output (6). Here again, there was a whole square operation!

Thank you!

 

restart

with(Physics)

[`*`, `.`, Annihilation, AntiCommutator, Antisymmetrize, Assume, Bra, Bracket, Cactus, Check, Christoffel, Coefficients, Commutator, CompactDisplay, Coordinates, Creation, D_, Dagger, Decompose, Define, Dgamma, Einstein, EnergyMomentum, Expand, ExteriorDerivative, Factor, FeynmanDiagrams, Fundiff, Geodesics, GrassmannParity, Gtaylor, Intc, Inverse, Ket, KillingVectors, KroneckerDelta, LeviCivita, Library, LieBracket, LieDerivative, Normal, Parameters, PerformOnAnticommutativeSystem, Projector, Psigma, Redefine, Ricci, Riemann, Setup, Simplify, SpaceTimeVector, StandardModel, SubstituteTensor, SubstituteTensorIndices, SumOverRepeatedIndices, Symmetrize, TensorArray, Tetrads, ThreePlusOne, ToFieldComponents, ToSuperfields, Trace, TransformCoordinates, Vectors, Weyl, `^`, dAlembertian, d_, diff, g_, gamma_]

(1)

Setup(signature = `-+++`, coordinates = (X = [t, r, theta, phi]))

`* Partial match of  'coordinates' against keyword 'coordinatesystems'`

 

`Default differentiation variables for d_, D_ and dAlembertian are: `*{X = (t, r, theta, phi)}

 

`Systems of spacetime Coordinates are: `*{X = (t, r, theta, phi)}

 

[coordinatesystems = {X}, signature = `- + + +`]

(2)

Setup(g_ = -dt^2+dr^2+r^2*dtheta^2+r(sin(theta))^4*dphi^2)

[metric = {(1, 1) = -1, (2, 2) = 1, (3, 3) = r^2, (4, 4) = r(sin(theta))^4}]

(3)

Setup(g_ = -dt^2+dr^2+r^2*dtheta^2+sin(theta)^2*r^2*dphi^2)

[metric = {(1, 1) = -1, (2, 2) = 1, (3, 3) = r^2, (4, 4) = sin(theta)^2*r^2}]

(4)

Setup(g_ = -dt^2+dr^2+r^2*dtheta^2+sin(theta)^2*r^2*dphi^2)

[metric = {(1, 1) = -1, (2, 2) = 1, (3, 3) = r^2, (4, 4) = sin(theta)^2*r^2}]

(5)

Setup(g_ = -exp(2*nu(r, theta))*dt^2+(exp(2*psi(r, theta)))(dphi-omega(r, theta)*dt)^2+(exp(2*mu(r, theta)))(dtheta)^2+exp(2*lambda(r, theta))*dr^2)

Error, (in Physics:-Setup) invalid subscript selector

 

Setup(g_ = -exp(2*nu(r, theta))*dt^2+(dphi-omega(r, theta)*dt)^2*exp(2*psi(r, theta))+exp(2*mu(r, theta))*dtheta^2+exp(2*lambda(r, theta))*dr^2)

[metric = {(1, 1) = -exp(2*nu(r, theta))+omega(r, theta)^2*exp(2*psi(r, theta)), (1, 4) = -omega(r, theta)*exp(2*psi(r, theta)), (2, 2) = exp(2*lambda(r, theta)), (3, 3) = exp(2*mu(r, theta)), (4, 4) = exp(2*psi(r, theta))}]

(6)

``


 

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