Positive bi-exponential interpolation

A function $bexp(cx)+dexp(fx)$ is called positive bi-exponential if $b>0, d>0,$ and $c e f.$ A positive bi-exponential function interpolates a function at equidistant nodes if and only if the function is strictly log-convex. A positive bi-exponential function is itself strictly log-convex. The sum of two not necessarily strictly log-convex functions is strictly log-convex if their derivatives are distinct.