Function Repository Resource:

# DirectionalD

Compute the directional derivative of a function

Contributed by: Wolfram Staff (original content by Alfred Gray)
 ResourceFunction["DirectionalD"][f,r,vars] computes the derivative of a function f in the direction r with variables vars.

## Details and Options

The directional derivative of a function f at the point p along an arbitrary vector represents the instantaneous rate of change of the function at that direction.
ResourceFunction["DirectionalD"] is a generalization of a partial derivative in which the rate of change is taken with respect to one of the variables, considering the rest as constant.
The directional derivative is formally defined as , where is the vector that indicates the direction.
An alternative definition of the directional derivative is taken to be with respect to a normalized arbitrary nonzero vector .
Other notations for the directional derivative are , , , , , , and .

## Examples

### Basic Examples (2)

Directional derivative of a function of two variables:

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Directional derivative of a function of three variables:

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### Scope (6)

Directional derivative with a zero component in one direction:

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A unit vector along direction (3/2,1):

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Without normalization:

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Evaluated at the point p=(3/2,1):

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Define a function:

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Compute the directional derivative:

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Directional derivative in the direction (-1,-1/2) evaluated at the point (-1,3/2):

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A plot of the directional derivative:

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Visualize directional derivatives over a surface:

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The directional derivative (red) and the gradient (blue):

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Enrique Zeleny

## Version History

• 2.0.0 – 01 October 2020
• 1.0.0 – 15 June 2020