  Calculating the primordial bispectrum predicted by a model of inflation and
comparing it to what we see in the sky is very computationally intensive,
necessitating layers of approximations and limiting the models which can be
constrained. Exploiting the inherent separability of the tree level in-in
formalism using expansions in separable basis functions provides a means by
which to obviate some of these difficulties. Here, we develop this approach
further into a practical and efficient numerical methodology which can be
applied to a much wider and more complicated range of bispectrum phenomenology,
making an important step forward towards observational pipelines which can
directly confront specific models of inflation. We describe a simple augmented
Legendre polynomial basis and its advantages, then test the method on
single-field inflation models with non-trivial phenomenology, showing that our
calculation of these coefficients is fast and accurate to high orders.
