What is an optimisation solver?

An optimisation solver is the engine that finds the best answer to a planning problem once someone has written it down as a mathematical model. Wikipedia defines optimisation as "the selection of a best element, with regard to some criteria, from some set of available alternatives". Buyers rarely meet a solver directly. They meet it inside a scheduling, cutting or haul-planning application whose model feeds it.

Model and solver

The model has an objective, such as maximise value or minimise lateness. It has decisions: what to make, when, on which line. And it has constraints: capacities, due dates, setup times, product rules. The solver searches the possible plans for the best one that respects every constraint. A missing constraint is a fault in the model, and no solver can fix it.

How to judge one

Two numbers matter. The first is the gap: how far the plan could be from the best possible. For large problems the true best is often unknown, so solvers prove a bound and report the distance to it. Gurobi's documentation, for one widely used solver, says its default stops "when the gap between the lower and upper objective bound is less than MIPGap times the absolute value of the incumbent objective value", with MIPGap set to 1e-4, or 0.01%. Applications often loosen that to answer faster.

The second is speed. Plans change when an order arrives or a machine goes down, and an application that takes an hour to re-plan can't keep up. For plans solved rarely, such as a long-term harvest schedule, a closer gap may be worth the wait.

In a timber business

Optimisation runs in bucking and sawing optimisers, log allocation, harvest scheduling, truck routing, and trim in paper and packaging. Many run inside equipment. Others need orders, inventory, capacity and costs from several systems, and are only as good as those inputs.

What to check

Ask which constraints are modelled, what gap the tool reports on your own problems, and how long a re-solve takes. Then compare its plans with what your planners would do, on the same days.

Quarri for sawmills is built around how a sawmill runs, from log intake to shipped order.

Quarri is an AI-native data platform for the timber supply chain. It connects buying, production, sales and inventory for forest management, sawmill, wood products and pulp, paper and packaging operators.