Reference desk / edition 2026.10
Implementation contracts
Version inputs, units, missing-data rules, licences and reproducible calculation artifacts.
Calculation references
Two-sided and one-way turnover
Measure traded capital fractions from aligned drifted and target weights under a stated convention.
Linear rebalance cost drag
Convert a symmetric per-side basis-point cost and traded weights into a one-period return approximation.
Detailed guides
Implementation contractsThe model card input contract: make valid inputs unambiguous
Specify shape, units, identity, numerical domains and rejection behavior before treating a mathematical example as reusable code.
Implementation contractsMissing data and alignment: decide what was actually observable
Keep missingness, stale observations, asynchronous timestamps and covariance sample selection visible in a calculation's input history.
Implementation contractsReproducible model artifacts: preserve the calculation, not just its answer
Build a checkable evidence bundle that distinguishes identical files, numerically equivalent outputs and independently verified arithmetic.
Implementation contractsModel version and change control: preserve what each result meant
Define compatibility for mathematical outputs, classify hypothetical changes and keep first-edition evidence distinct from proposed future releases.
Implementation contractsOpen source and data rights: separate the permissions in a reproduction kit
Inventory code, fixtures, documentation and external data separately, using primary licence texts rather than assuming public access grants redistribution rights.