potential

Potential of vector field

Syntax

potential(V,X)

potential(V,X,Y)

Description

potential(V,X) computes the potential of the vector field V with respect to the vector X in Cartesian coordinates. The vector field V must be a gradient field.

example

potential(V,X,Y) computes the potential of vector field V with respect to X using Y as base point for the integration.

example

Examples

Compute Potential of Vector Field

Compute the potential of this vector field with respect to the vector [x, y, z]:

syms x y z
P = potential([x, y, z*exp(z)], [x y z])

P =
x^2/2 + y^2/2 + exp(z)*(z - 1)

Use the gradient function to verify the result:

simplify(gradient(P, [x y z]))

ans =
        x
        y
 z*exp(z)

Specify Integration Base Point

Compute the potential of this vector field specifying the integration base point as [0 0 0]:

syms x y z
P = potential([x, y, z*exp(z)], [x y z], [0 0 0])

P =
x^2/2 + y^2/2 + exp(z)*(z - 1) + 1

Verify that P([0 0 0]) = 0:

subs(P, [x y z], [0 0 0])

ans =
     0

Test Potential for Field Without Gradient

If a vector field is not gradient, potential returns NaN:

potential([x*y, y], [x y])

ans =
NaN

Input Arguments

collapse all

`V` — Vector field
3-D symbolic vector of symbolic expressions or functions (default)

Vector field, specified as a 3-D vector of symbolic expressions or functions.

`X` — Input
vector of three symbolic variables

Input, specified as a vector of three symbolic variables with respect to which you compute the potential.

`Y` — Input
symbolic vector

Input, specified as a symbolic vector of variables, expressions, or numbers that you want to use as a base point for the integration. If you use this argument, potential returns P(X) such that P(Y) = 0. Otherwise, the potential is only defined up to some additive constant.

More About

collapse all

Scalar Potential of Gradient Vector Field

The potential of a gradient vector field V(X) = [v₁(x₁,x₂,...),v₂(x₁,x₂,...),...] is the scalar P(X) such that $V (X) = \nabla P (X)$ .

The vector field is gradient if and only if the corresponding Jacobian is symmetrical:

$(\frac{\partial v_{i}}{\partial x_{j}}) = (\frac{\partial v_{j}}{\partial x_{i}})$

The potential function represents the potential in its integral form:

$P (X) = \int_{0}^{1} (X - Y) \cdot V (Y + λ (X - Y)) d λ$

Tips

If potential cannot verify that V is a gradient field, it returns NaN.
Returning NaN does not prove that V is not a gradient field. For performance reasons, potential sometimes does not sufficiently simplify partial derivatives, and therefore, it cannot verify that the field is gradient.
If Y is a scalar, then potential expands it into a vector of the same length as X with all elements equal to Y.

Version History

Introduced in R2012a