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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of combinatorial optimization 2 (1998), S. 333-350 
    ISSN: 1573-2886
    Keywords: travelling salesman problem ; subtour patching ; combinatorial optimization ; computational complexity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider traveling salesman problems (TSPs) with a permuted Monge matrix as cost matrix where the associated patching graph has a specially simple structure: a multistar, a multitree or a planar graph. In the case of multistars, we give a complete, concise and simplified presentation of Gaikov's theory. These results are then used for designing an O(m3 + mn) algorithm in the case of multitrees, where n is the number of cities and m is the number of subtours in an optimal assignment. Moreover we show that for planar patching graphs, the problem of finding an optimal subtour patching remains NP-complete.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical methods of operations research 50 (1999), S. 9-16 
    ISSN: 1432-5217
    Keywords: Key words: Transportation problem ; permutable demand vector ; computational complexity ; minimum weight f-factor problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract. In this note we investigate the computational complexity of the transportation problem with a permutable demand vector, TP-PD for short. In the TP-PD, the goal is to permute the elements of the given integer demand vector b=(b 1,…,b n) in order to minimize the overall transportation costs. Meusel and Burkard [6] recently proved that the TP-PD is strongly NP-hard. In their NP-hardness reduction, the used demand values b j, j=1,…,n, are large integers. In this note we show that the TP-PD remains strongly NP-hard even for the case where b j∈{0,3} for j=1,…,n. As a positive result, we show that the TP-PD becomes strongly polynomial time solvable if b j∈{0,1,2} holds for j=1,…,n. This result can be extended to the case where b j∈{κ,κ+1,κ+2} for an integer κ.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of combinatorial optimization 3 (1999), S. 51-58 
    ISSN: 1573-2886
    Keywords: Steiner tree ; Kalmanson matrix ; circulant matrix ; computational complexity ; graph algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We investigate the computational complexity of two special cases of the Steiner tree problem where the distance matrix is a Kalmanson matrix or a circulant matrix, respectively. For Kalmanson matrices we develop an efficient polynomial time algorithm that is based on dynamic programming. For circulant matrices we give an $$\mathcal{N}\mathcal{P}$$ -hardness proof and thus establish computational intractability.
    Type of Medium: Electronic Resource
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