We prove that the problem STO of deciding whether or not a finite set E of term equations is subject to occur-check is in NP. E is subject to occur-check if the execution of the Martelli-Montanari unification algorithm gives for input E a set E ∪ {x = t}, where t = x and x appears in t. Apt et al. (
Permuted max-algebraic eigenvector problem is NP-complete
✍ Scribed by P. Butkovič
- Publisher
- Elsevier Science
- Year
- 2008
- Tongue
- English
- Weight
- 129 KB
- Volume
- 428
- Category
- Article
- ISSN
- 0024-3795
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✦ Synopsis
Let a ⊕ b = max(a, b) and a ⊗ b = a + b for a, b ∈ R := R ∪ {-∞} and extend these operations to matrices and vectors as in conventional linear algebra. The following eigenvector problem has been intensively studied in the past: Given A ∈ R n×n find all x ∈ R n , x / = (-∞, . . . , -∞) T (eigenvectors) such that A ⊗ x = λ ⊗ x for some λ ∈ R. The present paper deals with the permuted eigenvector problem: Given A ∈ R n×n and x ∈ R n , is it possible to permute the components of x so that it becomes a (max-algebraic)
eigenvector of A? Using a polynomial transformation from BANDWIDTH we prove that the integer version of this problem is NP-complete.
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