# User Data Functions

Since all of the User Data variables, intrinsic functions, operators and material properties that can be used in RS2 are listed in the Define User Data Function dialog, they will not be re-listed here. However, here are some points to remember:

Variables

In the Define User Data Equation dialog, under the Variables tab, it is noted that "d" can be added in front of any variable (e.g. "ds1") to denote the differential result, and also that "r" can be added in front of any variable to denote the reference result (e.g. "rs1"). The following example is given to clarify this situation:

Example (using variable s1, major principal stress):

If the Stage Settings for the view were Stage = 4 and Reference Stage = 2, then:

• Variable s1 = stage 4 results
• Variable rs1 = stage 2 results
• Variable ds1 = differential (stage 4 –stage 2) results (*see note below).

NOTE:

1. To use differential or reference stage variables, the Reference Stage in the Stage Settings option must be greater than zero (i.e. you must already be viewing differential data)
2. *DIFFERENTIAL PRINCIPAL STRESSES: In general, ds1 is NOT equal to s1 – rs1 (and ds3 is NOT equal to s3 – rs3). This is because the differential principal stresses are obtained by subtracting the stress tensors, and calculating the differential principal stress tensor, from which ds1 and ds3 are obtained. (This is necessary since simple subtraction of the principal stress magnitudes at each node would not take into account differences in orientation of the principal stresses, at different stages).
3. For all other variables, the differential result IS equal to the visible stage – reference stage values. For example, the differential strength factor variable dsf = sf – rsf.