# Response Variables

Model behavior is captured in terms of Response Variables.

These are the functions $\psi \left(...\right)$ , in the equations in the Optimization Problem Formulation section. The optimizer in MotionSolve works with Response Variables. Response Variables are used to define the cost and constraint functions for the optimization problem. The MotionSolve optimization toolkit provides a library of responses that you can use to define cost and constraint functions. You can, if you wish, create your own response variables and use it.

The following responses are available in MotionSolve: