Set the cosmology used (i.e., ).
where is the Hubble constant in km s–1 Mpc–1, is the deceleration parameter, and is the cosmological constant. If the cosmological constant is non-zerothen 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 , , and
XSPEC12> cosmo 100
XSPEC12> cosmo ,0
XSPEC12> cosmo ,,0.7
// Set a flat universe with