# Glossary

- D-optimal
- The state of an experimental design in which the determinant of the moment matrix X T X of the least squares formulation is maximized.
- Delimiter
- Symbol(s) to separate numeric fields in a text file. Typically spaces, tabs or commas.
- Dependent
- A function which is dependent on variables. Dependent variable.
- Design formula
- A simple mathematical expression which gives the response of a design when the design variables are substituted. See response surface.
- Design of Experiments
- See experimental design.
- Design parameter
- See design variable.
- Design sensitivity
- The gradient vector of the response. The derivatives of the response function in terms of the design variables. df /dxi.
- Design space
- A region in the n-dimensional space of the design variables (x1 through xn to which the design is limited. The design space is specified by upper and lower bounds on the design variables. Response variables can also be used to bound the design space.
- Design surface
- The response variable as a function of the design variables, used to construct the formulation of a design problem. (See also response surface, design rule).
- Design variable
- An independent design parameter which is allowed to vary in order to change the design. Symbolized by (xi or x (vector containing several design variables)).
- Discipline
- An area of analysis requiring a specific set of simulation tools, usually because of the unique nature of the physics involved, e.g. structural dynamics or fluid dynamics. In the context of MDO, often used interchangeably with solver.
- DOE
- Design of Experiments. See experimental design.
- DSA
- Design sensitivity analysis.