Maxima Function
psi (dis)
Computes the five Newman-Penrose coefficients psi[0]
...psi[4]
.
If psi
is set to true
, the coefficients are displayed.
See for an example.
These coefficients are computed from the Weyl-tensor in a coordinate base.
If a frame base is used, the Weyl-tensor is first converted to a coordinate
base, which can be a computationally expensive procedure. For this reason,
in some cases it may be more advantageous to use a coordinate base in the
first place before the Weyl tensor is computed. Note however, that
constructing a Newman-Penrose null tetrad requires a frame base. Therefore,
a meaningful computation sequence may begin with a frame base, which
is then used to compute lg
(computed automatically by cmetric
and then ug
. At this point, you can switch back to a coordinate base
by setting cframe_flag
to false before beginning to compute the
Christoffel symbols. Changing to a frame base at a later stage could yield
inconsistent results, as you may end up with a mixed bag of tensors, some
computed in a frame base, some in a coordinate base, with no means to
distinguish between the two.