Translations:Dictionary:Eikonal equation/7/en

Another form of the eikonal equation is written in terms of the ray direction vector $\mathbf {p} =(p_{1},p_{2},p_{3})$ where the gradient of traveltime (or slowness) vector $p_{i}={\frac {\partial \phi }{\partial x_{i}}}$ for $i=1,2,3$