  Simulation ensembles are a common tool in physics for understanding how a
model outcome depends on input parameters. We analyze an active particle
system, where each particle can use energy from its surroundings to propel
itself. A multi-dimensional feature vector containing all particles' motion
information can describe the whole system at each time step. The system's
behavior strongly depends on input parameters like the propulsion mechanism of
the particles. To understand how the time-varying behavior depends on the input
parameters, it is necessary to introduce new measures to quantify the
difference of the dynamics of the ensemble members. We propose a tool that
supports the interactive visual analysis of time-varying feature-vector
ensembles. A core component of our tool allows for the interactive definition
and refinement of new measures that can then be used to understand the system's
behavior and compare the ensemble members. Different visualizations support the
user in finding a characteristic measure for the system. By visualizing the
user-defined measure, the user can then investigate the parameter dependencies
and gain insights into the relationship between input parameters and simulation
output.
