where w is the equation of state parameter of dark energy, and assuming negligible neutrino mass (significant neutrino mass requires a more complex equation). The various Ω Ω parameters add up to 1 by construction. In the general case this is integrated by computer to give the expansion history a ( t ) and also observable distance–redshift relations for any chosen values of the cosmological parameters, which can then be compared with observations such as supernovae and baryon acoustic oscillations.