Sedona XPRESSion Evaluator Reference Guide

Define Variable VI

Declares a variable in the internal database for use in describing expressions.

error in (no error) describes any error conditions prior to this VIs execution.
variable name is a string of characters which may include any alphanumeric character plus the underscore ‘_’ and colon ‘:’ characters.
initialize? (F) specifies whether or not to initialize the internal database of user-defined variables. If TRUE, then all variable definitions currently in memory will be deleted. If FALSE, then variable name is appended to the internal database of user-defined variables.
unit definition describes the physical units (if any) associated with the variable variable name. You do not need to wire unit definition if you will not be performing any units checking. If unit definition is unwired, then variable name is interpreted as a pure number (i.e. dimensionless).

If you do wire unit defintion, then unit definition describes the units to be associated with the user variable. The required format for the custom unit definition is:

<conv factor> <unit string expression>

where <conv factor> is the number required to scale the units in <unit string expression> to the appropriate base units used by the XPRESSion Evaluator. <conv factor> will often be used to describe units outside the MKS standard. For example, the unit "inches" cannot be expressed exactly in powers of the MKS base units, so a conversion factor is required. Some simple unit definition strings are:

0.0254 m

N m

kg J in

Note that newtons (N) and joules (J) can themselves be decomposed into fundamental units, but the XPRESSion Evaluator will take care of that for you, so that you needn’t bother describing compound units it terms of the fundamental units only. Note also that the unit abbreviation must be used and not the full unit name.
variable type (Scalar: 0) indicates whether the variable to be defined is a scalar or an array.
error out contains error information. If the error in cluster indicated an error, the error out cluster contains the same information. Otherwise, error out describes this VIs error status.
index out
user variable