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Gradient of a Function
There is an easier way to find the directional derivatives of f(x, y) using the partial derivatives. It is convenient to combine the partial derivatives into a vector called the gradient of f. DEFINITION The gradient of a function z = f(x, y), denoted by grad z or grad f, is defined by In functional notation, grad f = f_{x}(a,b)i + f_{y}(a,b)j. Thus grad f is the vector valued function of two variables whose x and y components are the partial derivatives f_{x} and f_{y} (Figure 13.1.3). Sometimes the notation ∇f or ∇z is used for the gradient. Figure 13.1.3


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