Michael_Watson

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16 years, 35 days

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These are replies submitted by Michael_Watson

Thank you.  That is what I get for coding at 2 am.

 

Michael

@Torre 

Okay, I think I got it now.  I was trying to create the tetrad from scratch.  I see that D_r, D_x, D_y, and D_u represent the vectors.  I was looking for subscripts and indices.  Anyway, I modified your suggestions and got some results which are letting me move in the right direction.

I think for my purposes, I will explicitly define the spin coefficients with the NPSpinCoefficients command and work through the NP formalism that way.  I am using arbitrary functions within my [l,n,m,mbar], so it is a bit much to ask for NPRicciIdentities running on a laptop.

Again, thanks for the help.

 

Michael

@Torre 

Okay, I think I got it now.  I was trying to create the tetrad from scratch.  I see that D_r, D_x, D_y, and D_u represent the vectors.  I was looking for subscripts and indices.  Anyway, I modified your suggestions and got some results which are letting me move in the right direction.

I think for my purposes, I will explicitly define the spin coefficients with the NPSpinCoefficients command and work through the NP formalism that way.  I am using arbitrary functions within my [l,n,m,mbar], so it is a bit much to ask for NPRicciIdentities running on a laptop.

Again, thanks for the help.

 

Michael

I changed the array to VectorField and left out the rotations, but DGsetup still give me the same error.

 

Michael

I changed the array to VectorField and left out the rotations, but DGsetup still give me the same error.

 

Michael

Sorry, I should have been more specific.  Yes the help files are useful.  Here is what I type in

restart;
with(DifferentialGeometry); with(Tensor); with(Tools);
l := [0, 1, 0, 0]; n := [u, U, x, y]; m := [zeta1, omega, zeta3, zeta4]; mbar := complex(m);

Apply rotations leaving l and n fixed

m := exp(I*theta)*m; mbar := complex(m); n := A(r, u, x, y)*n; l := l/A(r, u, x, y);

DGsetup([l, n, m, mbar], MN, verbose);

 

I get the error

Error, (in DifferentialGeometry:-DGsetup) invalid arguments

 

I know that there is a problem with using the arrays, but I am trying to follow (Kinnersley 1969) to derive the Kerr metric.  Just as a check I started the first couple of steps by hand, but that becomes tedious very quickly. Thanks.

 

Michael

Sorry, I should have been more specific.  Yes the help files are useful.  Here is what I type in

restart;
with(DifferentialGeometry); with(Tensor); with(Tools);
l := [0, 1, 0, 0]; n := [u, U, x, y]; m := [zeta1, omega, zeta3, zeta4]; mbar := complex(m);

Apply rotations leaving l and n fixed

m := exp(I*theta)*m; mbar := complex(m); n := A(r, u, x, y)*n; l := l/A(r, u, x, y);

DGsetup([l, n, m, mbar], MN, verbose);

 

I get the error

Error, (in DifferentialGeometry:-DGsetup) invalid arguments

 

I know that there is a problem with using the arrays, but I am trying to follow (Kinnersley 1969) to derive the Kerr metric.  Just as a check I started the first couple of steps by hand, but that becomes tedious very quickly. Thanks.

 

Michael

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