restart;

with(DifferentialGeometry);
with(Tensor);

DGsetup([x, t], M1);

g := evalDG((dt &t dt) - t^2*(dx &t dx))
Geodesics()

I created a two dimensional cross-section of a spacetime described by this metric above. 

I would like to plot the geodesics in polar coordinates using the time t as the radius (normalized to our current time equal to unity).

That is, I would like to plot the geodesics starting at x=0, t=1 (x=0 maps to the top of the polar plot). X is the polar angle.

This plot is likely to map to this figure. Never mind the details of wiggles, or titles, etc.  I am new to maple and could use an initial push.

How to create a double underscore in a macbook air.  

I type G__[], the underscore disappears even on 1-D math.  I am using maple 2019.1, Mojave 10.14.6

I am trying to follow an example on geodesics 

with(Physics);

Setup(mathematicalnotation = true);
Setup(coordinates = X);

g_[];

I cannot reproduce the example because I cannot even create the syntax.

@Torre 

with(DifferentialGeometry);
with(Tensor);
with(LieAlgebras);
DGsetup([x, y], M);
g1 := evalDG(dx &t dx);
Christoffel(g1);
Error, (in DifferentialGeometry:-Tensor:-Christoffel) expected 1st argument to be a metric tensor. Received: _DG([["tensor", M, [["cov_bas", "cov_bas"], []]], [`...`]])

I still get an error.  I was able to succeed in another example (when I copied the whole maple example.

Somehow, I cannot get the correct syntax.

Any help would be welcome.  The only explanation is that somehow the definition of the neutral tensor operator is missing.