ar X iv : m at h . N A / 0 60 55 81 v 1 2 2 M ay 2 00 6 EVALUATING THE EVANS FUNCTION : ORDER REDUCTION IN NUMERICAL METHODS

ar X iv : m at h / 06 05 58 1 v 1 [ m at h . N A ] 2 2 M ay 2 00 6 EVALUATING THE EVANS FUNCTION : ORDER REDUCTION IN NUMERICAL METHODS

We consider the numerical evaluation of the Evans function, a Wronskian-like determinant that arises in the study of the stability of travelling waves. Constructing the Evans function involves matching the solutions of a linear ordinary differential equation depending on the spectral parameter. The problem becomes stiff as the spectral parameter grows. Consequently, the Gauss–Legendre method ha...

ar X iv : m at h / 06 05 58 1 v 2 [ m at h . N A ] 2 8 N ov 2 00 6 EVALUATING THE EVANS FUNCTION : ORDER REDUCTION IN NUMERICAL METHODS

We consider the numerical evaluation of the Evans function, a Wronskian-like determinant that arises in the study of the stability of travelling waves. Constructing the Evans function involves matching the solutions of a linear ordinary differential equation depending on the spectral parameter. The problem becomes stiff as the spectral parameter grows. Consequently, the Gauss–Legendre method ha...

ar X iv : m at h - ph / 0 60 50 74 v 1 2 9 M ay 2 00 6 BRYANT - SALAMON ’ S G 2 - MANIFOLDS AND THE HYPERSURFACE GEOMETRY

We show that two of Bryant-Salamon’s G2-manifolds have a simple topology, S \ S or S \ CP . In this connection, we show there exists a complete Ricci-flat (non-flat) metric on Sn \ Sm for some n − 1 > m. We also give many examples of special Lagrangian submanifolds of T ∗Sn with the Stenzel metric. The hypersurface geometry is essential in the argument.

ar X iv : h ep - p h / 04 02 19 0 v 2 2 6 M ay 2 00 4 1 Pentaquarks in the 10 F - and 10 F - plets

ar X iv : m at h / 04 11 14 0 v 2 [ m at h . N T ] 4 M ay 2 00 5 THE 3 x + 1 SEMIGROUP

The 3x + 1 semigroup is the multiplicative semigroup S of positive rational numbers generated by { 2k+1 3k+2 : k ≥ 0} together with {2}. This semigroup encodes backwards iteration under the 3x + 1 map, and the 3x + 1 conjecture implies that it contains every positive integer. This semigroup is proved to be the set of positive rationals a b in lowest terms with b 6≡ 0( mod 3), and so contains al...