Test constraints and compare the feasible combinations

Write the constraints at the whole-combination scope. Separate initial capital, initial operating expenditure and recurring operating envelopes where they are different decisions. Include later commitments when they bind: the year-three overhaul in an EAM.8 policy needs its funding, crew and service window at that time. A low initial outlay does not establish that later provision. Do not count a resource twice or assume unused funding must be spent.

Enumerate a small finite set of indivisible choices. For the CityWater shortlist, choose exactly one of two options for each of four stations and compare all sixteen. For a different question, the feasible no-work, single and combined choices depend on what service is mandatory. Remove combinations excluded by a supported prerequisite, technical condition or resource limit, retaining the reason. Obtain a feasible service-preserving calendar through EAM.11 where timing can defeat an otherwise eligible selection.

For a larger problem, select an optimization or scenario method whose objective, choices, constraints and interactions represent the actual question. Specify what is selectable, which selections imply or exclude others, dated resource use and the joint effects. Model contingent actions with the information available when each action is chosen; the combination cannot assume different early choices for future outcomes that are not yet known. A mathematical optimum applies to the represented set and basis.

Compare eligible combinations using the actual value criteria. When required service and other material consequences are equal, minimize total present cost. Otherwise preserve justified trade-offs or a non-dominated set. A cheaper programme that requires more scarce resources does not automatically dominate a dearer one.