  A continuum description is essential for understanding a variety of
collective phenomena in active matter. However, building quantitative continuum
models of active matter from first principles can be extremely challenging due
to both the gaps in our knowledge and the complicated structure of nonlinear
interactions. Here we use a novel physically-informed data-driven approach to
construct a complete mathematical model of an active nematic from experimental
data describing kinesin-driven microtubule bundles confined to an oil-water
interface. We find that the structure of the model is similar to the
Leslie-Ericksen and Beris-Edwards models, but there are significant and
important differences. Rather unexpectedly, elastic effects are found to play
no role in the experiments considered, with the dynamics controlled entirely by
the balance between active stresses and friction stresses.
