FA-91644 / Digital signal filters / Member archive

Linear-phase check skips the centre tap for antisymmetry · case 04

[1, 2, -1] is classified as type 3 although a nonzero centre breaks antisymmetry.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input integer taps. Strip leading and trailing zeros ("degenerate" if all zero). The trimmed support of length N is type 1/2 if symmetric (odd/even N), type 3/4 if antisymmetric (odd/even N), otherwise not linear phase. Return {"type", "group_delay": leading zeros + (N-1)/2 as a fraction string} or both None.

Why this case matters

Linear-phase type determines which responses an FIR can realize (e.g. no highpass for type 2); misclassification picks the wrong design.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random linear phase 2	`{"group_delay": "4", "type": 3}`	`{"group_delay": null, "type": null}`	Failed

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