In this note, we will review and extend some results from our previous work [8] where we introduced a novel approach to imperfectly transferable utility and unobserved heterogeneity in tastes, based on a nonlinear generalization of the Bernstein-Schrödinger equation. We consider an assignment problem where agents from two distinct populations may form pairs, which generates utility to each agent. Utility may be transfered across partners, possibly with frictions. This general framework hence encompasses both the classic Non-Tranferable Utility model (NTU) of Gale and Shapley [6], sometimes called the "stable marriage problem", where there exists no technology to allow transfers between matched partners; and the Transferable Utility (TU) model of Becker [1] and Shapley-Shubik [14], a.k.a. "optimal assignment problem," where utility (money) is additively transferable across partners.If the NTU assumption seems natural for many markets (including school choices), TU models are more appropriate in most settings where there can be bargaining (labour and marriage markets for example). However, even in those markets, there can be transfer frictions. For example, in marriage markets, the transfers between partners might take the form of favor exchange (rather than cash), and the cost of a favor to one partner may not exactly equal the benefit to the other.In [8], we thus developped a general Imperfectly Transferable Utility model with unobserved heterogeneity, which includes as special cases the classic fully-and non-transferable utility models, but also extends to collective models, and settings with taxes on transfers, deadweight losses, and risk aversion. As we argue in the present note, the models we consider in [8] obey a particularly simple system of equations we dubbed "Nonlinear Bernstein-Schrödinger equation". The present contribution present a general result for the latter equation, and also derives several consequences. The main result is derived in Section 1. Section 2 and Section 3 consider equilibrium assignment problems with and without heterogeneity. Finally, we provide a discussion of our results in Section 4.