Checks and diagnostics

The eight checks

study.check() (and every stochlift run) computes these with the solver. None needs a reference answer.

Check	What it catches
builder_deterministic	the builder uses random numbers or hidden state
uncertainty_reaches_model	a data key named as uncertain does not change the model
stage_split	no first-stage variables, or no recourse variables
first_stage_rows_stable	uncertain data constrains first-stage variables directly
single_scenario_reduction	with one scenario the lift must equal the deterministic model
bound_ordering	WS ≤ RP ≤ EEV (for minimization)
decomposition_consistency	the extensive-form optimum equals the scenario-by-scenario cost of its first stage
mean_value_recourse	the mean-value decision is infeasible in some scenario

stochlift run exits with status 1 when a check fails, so it can guard a pipeline.

What the checks cannot do

They verify that the lift is consistent with your model, not that the stage split matches how decisions are made in practice. The bound ordering holds for any split. A person must review the spec.

When there is no solution

If the stochastic program is infeasible, StochLift says why in terms of your data.

Scenarios infeasible on their own. The deterministic model has no solution for some scenarios' data, so no stochastic program over them can work:

1 of 4 scenarios have no optimal solution even when solved on their own (infeasible), so no
stochastic program over them can be solved.
  scenario 2: demand = 130 (mean 77.5)
The deterministic model itself has no solution for these data. Typical fixes: allow shortfalls
with slack variables at a penalty cost (unmet demand, overtime, outsourcing) in the deterministic
model, or narrow the distributions (min/max under scenarios.distributions).

No common first stage. Every scenario has a solution, but no single first-stage decision is feasible in all of them (the recourse is not complete). StochLift adds scenarios one at a time and names a pair that already conflicts. The errors are stochlift.diagnose.ScenarioInfeasible and stochlift.diagnose.NoCommonFirstStage; both carry the scenario indices in .scenarios.