Source code for einsteinpy.symbolic.predefined.davidson
from sympy import Rational, diag, symbols
from einsteinpy.symbolic.metric import MetricTensor
[docs]
def Davidson():
"""
Davidson's cylindrically symmetric radiation perfect fluid universe
Davidson, J. Math. Phys., v32, p1560, (1991)
"""
coords = symbols("t r z phi")
t, r, z, phi = coords
expr = (1 + r**2) ** Rational(2, 5)
metric = diag(
-(expr**3),
t ** Rational(4, 3) * expr,
t ** Rational(-2, 3) / expr,
t ** Rational(4, 3) * r**2 / expr,
).tolist()
return MetricTensor(metric, coords, "ll", name="DavidsonMetric")