In parametric optimization, the simulation model is described by variable parameters. These can define the geometry, such as the length of an element or the number of elements, material properties, or other physical effects such as frequency. Parametric optimization is often used to tune a previously developed design. In non-parametric optimization, as known as shape or topology optimization, the user defines the requirements and constraints of the design, such as a load to bear while minimizing weight. The optimizer then finds configurations of material in the design space that meet these requirements. Non-parametric optimization is often used to generate clean-sheet designs.