I have a function $f(x,t;k)$, a starting point $x_0$, a gradient $\operatorname{Grad}(f)$, and an equilibrium point $x^*$. I can adjust the parameter $k$ freely, and I know that for any $k$ the process will eventually reach $x^*$.
I want to know which value of $k$ will produce a trajectory that takes me to $x^*$ in the shortest time possible.
What kind of a differential equation problem is this? Is there a canonical solution? Is there a reference somewhere I can check to get more information?