enumeration of the number of spanning trees in some ... - Toubkal
enumeration of the number of spanning trees in some ... - Toubkal
enumeration of the number of spanning trees in some ... - Toubkal
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7.3. Formulae for <strong>the</strong> Number <strong>of</strong> Spann<strong>in</strong>g Trees <strong>in</strong> a Maximal Planar Map 131Numerical results The Table 7.2 illustrates <strong>some</strong> <strong>of</strong> <strong>the</strong> values <strong>of</strong> <strong>the</strong> <strong>number</strong> <strong>of</strong> <strong>spann<strong>in</strong>g</strong><strong>trees</strong> <strong>in</strong> <strong>the</strong> sequence <strong>of</strong> planar maps, <strong>the</strong> Fan planar maps τ(F n ) and τ(G n ), byus<strong>in</strong>g <strong>the</strong> formula given <strong>in</strong> Theorem 7.3.5:n 2 3 4 5 6 7 8 9 10τ(F n ) 2 8 30 112 418 1560 5822 21728 81090τ(G n ) 1 5 19 71 265 989 3691 13775 51409Table 7.2: Some values <strong>of</strong> τ(F n ) and τ(G n )Let E n be a maximal planar map shown <strong>in</strong> Figure. 7.7. If we delete <strong>the</strong> edge e = v 1 v 2 <strong>of</strong>E n , we obta<strong>in</strong> <strong>the</strong> crystal planar map C n with n vertices (see Figure. 7.12).Figure 7.12: The crystal planar map C nTheorem 7.3.6 (A crystal planar map) The complexity <strong>of</strong> <strong>the</strong> crystal planar map C n(see Figure. 7.12) is given by <strong>the</strong> follow<strong>in</strong>g formula:τ(C n ) = 12 √ 3 (n − 2) ((2 + √ 3) n−2 − (2 − √ 3) n−2 ), n ≥ 3.Pro<strong>of</strong>: By Theorem 4.3.11, we have: τ(E n ) = τ(E n −e)+τ(E n .e), s<strong>in</strong>ce τ(E n −e) = τ(C n )and τ(E n .e) = τ(F n ) (see Figure. 7.13):<strong>the</strong>n τ(C n ) = τ(E n ) − τ(F n ). We replace by <strong>the</strong> value <strong>of</strong> τ(E n ) from Theorem 7.3.3 and<strong>the</strong> value <strong>of</strong> τ(F n−1 ) from Theorem 7.3.5, thus our result follows.□