Set the cosmology used (i.e., , , and ).
where <> is the Hubble constant in km/s/Mpc, <> is the deceleration parameter, and <> is the cosmological constant. If the cosmological constant is non-zero then at present XSPEC requires that the universe is flat. In this case the value of <> will be ignored and XSPEC will assume that . The default values are <> = 70, <> = 0.0, and <> = 0.73
// Set <>= 100 km/s/Mpc
// Set <>= 0
// Set a flat universe with <>= 0.7