Sturm-Liouville type. As an application, we consider an infinite square well in one dimension
in which the mass is a function of the position. Two situations are studied, one in which the
mass is a differentiable function of the position depending on a parameter $ b $. In the
second one the mass is constant except for a discontinuity at some point. When the
parameter $ b $ goes to infinity, the function of the mass converges to the situation described …