Physics[Vectors][Identify]  identify the vector character of an expression in the context of the Physics[Vectors] subpackage's conventions

Calling Sequence


Identify(A)


Parameters


A



any algebraic (vectorial or scalar) expression





Description


•

Identify returns a number between 0 and 7, related to the vector classification of its argument: 0 = scalar, 1 = cartesianvector, 2 = cylindricalvector, 3 = sphericalvector, 5 = nonprojected vector, 6 = can be cartesian or cylindrical (projected over the z axis), 7 = can be cylindrical or spherical (projected over the direction). This command is used by the commands of the Physics[Vectors] subpackage before proceeding with the computations; it can be used to check how is the package interpreting an expression or as tool in the context of other programs using Physics[Vectors].

•

The %Identify is the inert form of Identify, that is: it represents the same mathematical operation while holding the operation unperformed. To activate the operation use value.

•

Note that the representation for a vector implemented in the Physics[Vectors] subpackage is not a matrix (list of components), but an algebraic expression, as either a first degree polynomial in the unit vectors with no independent term, or a symbol with a predefined postfix: the underscore, (to change this default postfix see Physics/Setup). The classification of a projected vector in this context is made taking into account the following conventions:

()

=

cartesian unit vectors,

(
)

=

cylindrical unit vectors,

(
)

=

spherical unit vectors



•

The classification of a nonprojected vector or vector function depends entirely on its name, i.e., on whether it ends with _(a mimicry of the arrow over a letter), as in or

•

Concerning the coordinates, the conventions are:

()

=

cartesian coordinates,

(
)

=

cylindrical coordinates,

(
)

=

spherical coordinates




NOTE: these variables x, y, z, , and , as well as _i, _j, _k, , and , respectively used to represent the coordinates and the unit vectors, are automatically protected when the Physics[Vectors] subpackage is loaded.



Examples


>


 (1) 
>


 (2) 
The input for Identify is an algebraic (vectorial or scalar) expression. The output is a related number.
"A" is a scalar and "A_" is a nonprojected Vector.
>


 (3) 
>


 (4) 
A cartesian Vector.
>


 (5) 
A cylindrical Vector.
>


 (6) 
A spherical Vector.
>


 (7) 
A cartesian or cylindrical Vector.
>


 (8) 
A cylindrical or spherical Vector.
>


 (9) 
The divergence of a Vector is a scalar.
>


 (10) 
The curl of a Vector is a Vector.
>


 (11) 
The Laplacian of a Vector is a Vector.
>


 (12) 
>




See Also


&x, +, ., ChangeBasis, Component, Curl, diff, DirectionalDiff, Divergence, Gradient, Laplacian, Nabla, Norm, Physics, Physics conventions, Physics examples, Physics[Vectors]

