9.5 Directional Derivative
INTRODUCTION
We saw in the last section that for a function f of two variables x and y, the partial derivatives ∂z/∂x and ∂z/∂y give the slope of the tangent to the trace, or curve of intersection of the surface defined by z = f(x, y) and vertical planes that are, respectively, parallel to the x- and y-coordinates axes. Equivalently, we can think of the partial derivative ∂z/∂x as the rate of change of the function f in the direction given by the vector i, and ∂z/∂y as the rate of change of the function f in the j-direction. There is no reason to confine our attention to just two directions. In this section we shall see how to find the rate of change of a differentiable function in any direction. See FIGURE 9.5.1
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access