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Proof of `Interval scheduling is fixed-parameter tractable for the machines and the largest processing time` (1st statement)

groundedproofs/Lax470956Proofs/Theorem3Fpt.lean · lax-470956

What this proof establishes

no assumptions

Assuming the claims on the left, the claim on the right holds — checked by the archive's pipeline. Proof code is not displayed here.

Read the Lean proof on GitHub

Description

The explicit bound of the first form is stated for the words that leave room for the table. Fixed-parameter tractability is stated for every word whose entries fit, and there the table may not be addressable: a machine with 2w2 ^ w cells cannot hold (pmax+1)m(p_max + 1) ^ m entries when that exceeds 2w2 ^ w, although every entry of the word is a word.

The program first computes min((pmax+1)m)(x+1)min ((p_max + 1) ^ m) (|x| + 1) by repeated multiplication, testing each step by a division so that no intermediate value exceeds x+1|x| + 1, and compares it with x|x|.

If the table has at most x|x| entries, the sweep of the first form runs unchanged, within 1000(pmax+1)m(m+1)(x+1)1000 · (p_max+1)^m · (m+1) · (|x|+1) instructions.

Otherwise x<(pmax+1)m(k+1)k|x| < (p_max + 1) ^ m ≤ (k + 1) ^ k, where k=m+pmaxk = m + p_max is the parameter, so the word, and with it the number of jobs nn, is bounded by a function of the parameter alone. The program then tries every schedule. An odometer of nn digits in base m+1m + 1 runs through them, each digit naming a machine or rejecting the job. Each string is checked against the word: every job on an eligible machine, no two overlapping jobs on one machine, and the weight added up with a cap at the threshold. There are (m+1)n(m + 1) ^ n strings, each tested in time polynomial in the length, and nxn ≤ |x|.

The function of the parameter is gk=4000(k+1)(k+1)k(k+1)((k+1)k)g k = 4000 · (k+1) · (k+1)^k · (k+1)^((k+1)^k), much larger than the (mpmax)2m(m · p_max)^{2m} of the first form, which is the cost where the table fits.