FA-69175 / Tide and marine navigation tables / Member archive

Slack water from current samples: Slack is interpolated with the wrong velocity ratio · case 05

Slack times are mirrored inside the sample interval.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [ts, vs]: sample times (minutes) and signed current (flood positive). Zero samples are skipped; a slack occurs between consecutive nonzero samples of opposite sign. With no zero samples in between, slack time is linearly interpolated; across a run of zero samples it is the midpoint of the zero run. Times round half up to minutes; the label says which stream begins. Return [[minute, "flood-begins"|"ebb-begins"], ...].

Why this case matters

Tide tables and passage plans turn published predictions into go/no-go decisions about depth, clearance and timing.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
slack water from current samples [[0, 60, 120, 180, 240], [-0.9, -0.3, 0.2, 0.0, -0.4]]	`[[84, "flood-begins"], [180, "ebb-begins"]]`	`[[96, "flood-begins"], [180, "ebb-begins"]]`	Failed

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