gradient vector field

例句：

1. 1. The gradient of the roadis steep.
   这条路的坡度很大。
2. 2. Thegradient of the temperature changes with altitude.
   温度随海拔变化而变化。
3. 3. Thegradient of the river isdetermined by its flow rate anddepth.
   河流的流速和深度决定了其梯度。