A position-dependent-mass oscillator makes the standard entropy math too hard to solve directly, so the calculation gets punted to an asymptotic limit that behaves like an ordinary harmonic oscillator. Momentum-space entropies, though, come out exact, no approximation needed, and both versions converge to Shannon entropy as expected.

— via arXiv — Physics, Dorcas A. Addo, Daniel Sabi-Takou, Eugene Adjei, Lat'evi M. Lawson