External variables

External variable idea

External variables represents results obtained by call external software (see External call). It can be for example displacements or stress extracted from finite element program output file. Esternal can also to represent derivatives of given result with respect to input variable (design or random) providing external software can compute derivatives (sensitivity analysis).

External variables table

External variable table contains set of external variables already defined in a project. User can add new design variable by pressing "Add" button. If Add is pressed, external variable definition dialog (described below) appears on the screen. If an user doubleclick on a variable in variables table design variable dialog is displayed in modification mode. It allows for update definition for given variable. User can also delete selected variables or duplicate it. It is very useful when several variables have to be defined with similar parameters.

"External variables table"

Design variable definition dialog

External variable definition dialog is presented below. To define random variables user have to do as follows:

  • Type unique name (taking into account any variables defined in the project)
  • Check "is derivative" if defined variable is derivative. Otherwise uncheck.
  • Select proper derivatives (if applicable).
Note that: if defined variable has computed derivatives (external software is able to deliver sensitivities) external variables represents derivatives have to be defined before the variable. "by finite difference" option means that if gradient is need it will be computed by finite difference method. Perturbation value can be estimated automatically or entered by user in variable definition dialog box (see Random variables, Design variables )

"External variables table"

External variables in main tree

External variables are also represented by items in main tree to open design variables list user can click on "External variables" item in the tree (in the picture below). Other way to open tis list is to click icon "Design variables icon" in the toolbar or in main menu Manage/Design variables.

"External variables table"