Classify all probability density functions φ:R→[0,∞) such that, for every integer n≥1 and every l1,…,ln∈R, the function
L(x)=i=1∏nφ(x−li)
is integrable, has a finite first moment, and has a unique global maximizer l′, with this maximizer equal to the centroid l′′ of L, where
l′′=∫−∞∞L(x)dx∫−∞∞xL(x)dx.