An optimal bound for the ratio between ordinary and uniform exponents of Diophantine approximation

We provide a lower bound for the ratio between the ordinary and uniform exponent of both simultaneous Diophantine approximation and Diophantine approximation by linear forms in any dimension. This lower bound was conjectured by Schmidt and Summerer and already shown in dimension $2$ and $3$. This lower bound is reached at regular graph presented in the context of parametric geometry of numbers, and thus optimal.