Duf(function, [varlist], [point], [direction])

[varlist]
If no value is given the default value is [x,y,z].

[point]
If given the directional derivative is calculated at that point. If not, then [x, y, z] is used.

[direction]
If given the derivative is calculated at the given point in the direction of the given vector. If no direction is given the vector [1, 1, 1] is assumed.

Description

Calculates the directional derivative of a given function.

Examples

Duf(x^2*y^2*z^2, [x, y, z], [1, 2, 3], [1, 1, -2])
Duf(x^2*y^2*z^2)
Duf(f(x, y, z))
Duf(x^2*y*z, [x, y, z], [1, -1, 1], [4, 0, -3])
Duf(3x^2-3y^2, [x, y], [1, 2], [0, 1])
Duf(sqrt(x^2+y^2), [x, y, z], [0, -2, 1], [2, 2, 1])
Duf(sin(x)+cos(y)+sin(z), [x, y, z], [@pi, 0, @pi], [@pi, @pi, 0])

References

http://mathworld.wolfram.com/DirectionalDerivative.html
http://en.wikipedia.org/wiki/Directional_derivative
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