id: ev title: Damage as a distribution, not a mean status: open dependsOn: [protocol] exitCriterion: > Fire allocation is chosen on P(threshold), and the calculator is tested against hand-computed cases. #

ev #

At a to-hit of 11 a PPC has an expected 0.83 damage and an actual outcome of "nothing, 92% of the time". Overkill decisions need the distribution; the mean says a Locust needs two PPCs when it needs many more. (The figure was written here against a to-hit of 10, which 2d6 reaches one time in six, not one in twelve.)

The calculator lives in crates/sds-core/src/ev.rs. Nothing calls it yet.

• Per-shot PMF over integer damage: 1 - P(hit) at zero, the rest across the cluster table for the rack size, times per-missile damage
• Convolve shots for an allocation; memoise on (rack, per-missile damage, to-hit, cluster modifier)
• Query it for mean, p50, p90, P(>=20) (the piloting-roll cliff)
• Carry expected packet count alongside, for punch-versus-sandblast
• P(kill) and P(breach), against the location the damage reaches rather than the target's total. at_least(threshold) is still the whole of the arithmetic; what was missing was not the threshold but the distribution to apply it to. EvCache::location_allocation carries the per-location compound distribution, and hitloc supplies the shares. See plan/features.md for the size of the error this removed
• Feed AMS into the cluster modifier. The key has the field and the roll applies it; nothing on the wire says a target mounts AMS
• Force-level greedy allocation against the concave value curve. Waits on force-level assignment machinery, which does not exist yet. Greedy on a submodular objective is within 1-1/e; any search over subsets is exponential
• Declare high-concentration weapons first. Declaration order is resolution order - TWGameManager.handleAttacks walks getAttacksVector() calling handle, with no sort or comparator in it - and the ladder already orders a declaration by descending damage per packet, which is "most concentrated first". That sort exists to choose which subsets to offer, so the property was incidental; it is now pinned by a test that fails if the ladder is reordered. The guarantee is over one declaration: the attacks vector interleaves both sides in arrival order, so a friendly gun opening a location for a friendly cluster weapon is reliable and an enemy's position in that vector is not. Ordering by p_breach rather than by packet size is a possible refinement and is not measured.