We define the parameterization b = 2(1 − α), δτ = α/D, which determines μ via eq. (3). Candidate purity and ploidy solutions for a tumor sample are identified by optimization of eq. (5) with respect to b and δτ. Calculation of eq. (5) requires estimates of θ and σH, which are not known a priori. We make an approximation (scale-separation) assuming that locations of the modes of eq. (5) are invariant to moderate fluctuations in these parameters. A provisional likelihood for each xi may then be calculated by
