Topic 10 · Modelling & Simulation (HL Option)

Reality too DANGEROUS · EXPENSIVE · SLOW · IMPOSSIBLE. Often multiple reasons combined.

All models are wrong; some are useful. The question is 'useful for THIS decision?'

What CHANGES over time. Position, velocity, infected count. The state of the system.

FIXED values you choose. Gravity g, bounce coef e, infection rate β. Tune the dynamics.

Equations or logic relating state at t to t+Δt. v_new = v + g·dt. The dynamics.

Simplifications you've MADE. Air drag = 0. Uniform population mixing. ALWAYS list them.

'Built it RIGHT?' — code matches spec. Tools: unit tests, code review.

'Built the RIGHT thing?' — model matches reality. Tools: hindcasting, held-out data, expert review.

Run model on a KNOWN case first (e.g. analytic answer). If it fails, don't trust complex predictions.

Use the SMALLEST model that answers your question. More parameters = more uncertainty + bugs + slowness.