Hullzie16

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These are questions asked by Hullzie16

Suppose I have a metric g, and I want to perform a conformal transformation g = exp(2Phi(X))*g, is there a straightforward way to do this for curvature quantitieies (Christoffel, Ricci Scalar etc)? I was able to do it rather easily for the Christoffel symbols, as seen below, but it required me making a substitution for each index pair. While this isn't horrible, it would be nice if there was a way to do it without this procedure.

** Edited to make it Phi(X) 

restart;

with(Physics):CompactDisplay(Phi(X)):

Phi(X)*`will now be displayed as`*Phi

(1)

Setup(metric=arbitrary):

_______________________________________________________

 

`Systems of spacetime coordinates are:`*{X = (x1, x2, x3, x4)}

 

`Default differentiation variables for d_, D_ and dAlembertian are:`*{X = (x1, x2, x3, x4)}

 

`The arbitrary metric in coordinates `*[x1, x2, x3, x4]

 

`Signature: `(`- - - +`)

 

_______________________________________________________

 

Physics:-g_[mu, nu] = Matrix(%id = 36893488152300428092)

(2)

Christoffel[~alpha,beta,nu,definition]

Physics:-Christoffel[`~alpha`, beta, nu] = (1/2)*Physics:-g_[`~alpha`, `~mu`]*(Physics:-d_[nu](Physics:-g_[mu, beta], [X])+Physics:-d_[beta](Physics:-g_[mu, nu], [X])-Physics:-d_[mu](Physics:-g_[beta, nu], [X]))

(3)

Simplify(eval((3),[g_[mu,beta]=exp(2*Phi(X))*g_[mu,beta],g_[mu,nu]=exp(2*Phi(X))*g_[mu,nu],g_[beta,nu]=exp(2*Phi(X))*g_[beta,nu]]))

Physics:-Christoffel[`~alpha`, beta, nu] = exp(2*Phi(X))*(Physics:-d_[nu](Phi(X), [X])*Physics:-g_[beta, `~alpha`]+Physics:-d_[beta](Phi(X), [X])*Physics:-g_[nu, `~alpha`]-Physics:-d_[`~alpha`](Phi(X), [X])*Physics:-g_[beta, nu]+Physics:-Christoffel[`~alpha`, beta, nu])

(4)

expand((4))

Physics:-Christoffel[`~alpha`, beta, nu] = (exp(Phi(X)))^2*Physics:-d_[nu](Phi(X), [X])*Physics:-g_[beta, `~alpha`]+(exp(Phi(X)))^2*Physics:-d_[beta](Phi(X), [X])*Physics:-g_[nu, `~alpha`]-(exp(Phi(X)))^2*Physics:-d_[`~alpha`](Phi(X), [X])*Physics:-g_[beta, nu]+(exp(Phi(X)))^2*Physics:-Christoffel[`~alpha`, beta, nu]

(5)
 

 

Any thoughts appreciated, thank you!

MyConformal.mw

I have a procedure that I am trying to run that would be an improvement/more sophisticated way of solving a problem that I have previously solved. When I try and run my procedure I am getting an error, and from what I gather with the error is that there are some values when inserted into my procedure that cannot be evaluated. Just for context it is a procedure that contains numerical solutions to a system of DEs and and contains inequalities. 

I would like to know is there an easy method to figure out what values are giving me this error? 

Or a follow up, is there something wrong with my procedure that is giving me this error? I have included some commentary in my workshet as well to hopefully make everything clear. 

Thanks. 

Proc_Error.mw

I have a differential equation which I am looking for a series solution in inverse powers of r. I am doing this by matching inverse powers between the RHS and LHS of the differential equation and then finding the coefficient in the series solution that would solve this. I have written a little procedure which returns the coefficients, I am just curious if there is a command that will do this for me or if i can improve on this technique? I tried the Solve command in PDETools but it just kept evaluating and did not return an answer. 

Thanks in advance. 

 

EDIT: More detail provided in the first reply. 

coefficient_question.mw

I have a thirder order ODE with non polynomial coefficients and I naively thought to try dsolve for fun to see what happens and Maple returned DESol with a second order differential equation and an arbitrary coefficient. I know Maple outputs DESol when it cannot find a solution similar to RootOf but the arbitrary constant is what is throwing me off. 

I am unsure how to interpret this, if a particular solution is found I could reduce the order and see how I could get with the second order ODE but maple doesn't produce a particular solution when I run that command. 

DESol_Question.mw

I am running Maple 2023 - yes I should update - and I found a weird "bug" if you could call it that. For different versions of the Physics package I am getting different answers on the same problem. 
 

This is what I was getting when I run Version 1410:

restart;

with(Physics):

 

Physics:-Version()

`The "Physics Updates" version in the MapleCloud is 1744. The version installed in this computer is 1410 created 2023, March 11, 12:59 hours Pacific Time, found in the directory /Users/b2hull/maple/toolbox/2023/Physics Updates/lib/`

(1)

Setup(mathematicalnotation=true):

g_[arbitrary]:

_______________________________________________________

 

`Systems of spacetime coordinates are:`*{X = (x1, x2, x3, x4)}

 

`Default differentiation variables for d_, D_ and dAlembertian are:`*{X = (x1, x2, x3, x4)}

 

`Setting `*lowercaselatin_is*` letters to represent `*space*` indices`

 

`The arbitrary metric in coordinates `*[x1, x2, x3, x4]

 

`Signature: `(`- - - +`)

 

_______________________________________________________

(2)

LG :=(g_[~mu,~nu]*Ricci[mu,nu])*sqrt(-%g_[determinant]);

Physics:-g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]*(-%g_[determinant])^(1/2)

(3)

SG:=Intc(LG,X)

Int(Int(Int(Int(Physics:-g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]*(-%g_[determinant])^(1/2), x1 = -infinity .. infinity), x2 = -infinity .. infinity), x3 = -infinity .. infinity), x4 = -infinity .. infinity)

(4)

EQ:=Fundiff(SG,%g_[~delta,~gamma])/sqrt(-%g_[determinant])

((1/2)*%g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]*%g_[delta, gamma]*%g_[determinant]/(-%g_[determinant])^(1/2)+Physics:-Ricci[mu, nu]*(-%g_[determinant])^(1/2)*%g_[delta, `~mu`]*%g_[gamma, `~nu`])/(-%g_[determinant])^(1/2)

(5)

Simplify(subs(%g_=g_,EQ))

-(1/2)*Physics:-g_[delta, gamma]*Physics:-Ricci[nu, `~nu`]+Physics:-Ricci[delta, gamma]

(6)

 

 

 

And this is what I get if I used the latet update for 2023, Version 1683:

restart;

with(Physics):

Physics:-Version();

`The "Physics Updates" version in the MapleCloud is 1744. The version installed in this computer is 1683 created 2024, March 6, 17:43 hours Pacific Time, found in the directory /Users/b2hull/maple/toolbox/2023/Physics Updates/lib/`

(1)

Setup(mathematicalnotation=true):

g_[arbitrary]:

_______________________________________________________

 

`Systems of spacetime coordinates are:`*{X = (x1, x2, x3, x4)}

 

`Default differentiation variables for d_, D_ and dAlembertian are:`*{X = (x1, x2, x3, x4)}

 

`Setting `*lowercaselatin_is*` letters to represent `*space*` indices`

 

`The arbitrary metric in coordinates `*[x1, x2, x3, x4]

 

`Signature: `(`- - - +`)

 

_______________________________________________________

(2)

LG :=(g_[~mu,~nu]*Ricci[mu,nu])*sqrt(-%g_[determinant]);

Physics:-g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]*(-%g_[determinant])^(1/2)

(3)

SG:=Intc(LG,X)

Int(Int(Int(Int(Physics:-g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]*(-%g_[determinant])^(1/2), x1 = -infinity .. infinity), x2 = -infinity .. infinity), x3 = -infinity .. infinity), x4 = -infinity .. infinity)

(4)

EQ:=Fundiff(SG,%g_[~delta,~gamma])/sqrt(-%g_[determinant])

-(1/2)*%g_[delta, gamma]*Physics:-g_[`~mu`, `~nu`]*Physics:-Ricci[mu, nu]

(5)

Simplify(subs(%g_=g_,EQ))

-(1/2)*Physics:-g_[delta, gamma]*Physics:-Ricci[nu, `~nu`]

(6)

 

 

Strange right? I bring this up because it makes me wonder about potential errors in other computations...

The answer - equation 6 - in 1410 is the correct answer. This is simply a derivation of the Einstein Tensor. 

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