# Define Input Variables

An input variable is a system parameter that influences the system performance in the chosen output response. It is an object that is varied by the study based on certain rules.

Input variables can be of different types with respect to their physical and/or numerical nature. Physically they can be dimensions, material properties, locations, and so on. Numerically they can be continuous numbers, discrete, integer, real, strings.

You can associate an input variable to a particular model parameter. Two input variables cannot be associated with the same model parameter. An input variable does not always need to be associated to a model parameter.

- Optimization Input Variables
- Input variables should be independent of each other. Selection of input
variables may not be unique. In Figure 1, either r
_{i}and r_{o}or r_{i}and t can be selected as input variables.Note: The selection of input variables affects the Optimization process.For a larger search space and increased flexibility in the solution, you need to use as many independent input variables as possible. For computational affordability, you need to identify and only include the most important input variables.It is recommended that you use as many independent input variables as possible to promote a large search space and increased flexibility. However, for computational affordability you should only include the most important input variables.