►Generalized hypergeometric functions and Appell functions appear in the evaluation of the so-called Watson integrals which characterize the simplest possible latticewalks.
They are also potentially useful for the solution of more complicated restricted latticewalk problems, and the 3D Ising model; see Barber and Ninham (1970, pp. 147–148).
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►where and the square roots are real and positive when the lattice is rectangular; otherwise they are determined by continuity from the rectangular case.
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►The lattice invariants are defined by
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►The lattice roots satisfy the cubic equation
…and are denoted by .
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►Let , or equivalently be nonzero, or be distinct.
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►Conversely, , , and the set are determined uniquely by the lattice
independently of the choice of generators.
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►(23.10.8) continues to hold when , , are permuted cyclically.
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►Also, when is replaced by the lattice invariants and are divided by and , respectively.
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and are meromorphic functions with poles at the lattice points.
is even and is odd.
…The function is entire and odd, with simple zeros at the lattice points.
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►The Weierstrass function plays a similar role for cubic potentials in canonical form .
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►Airault et al. (1977) applies the function to an integrable classical many-body problem, and relates the solutions to nonlinear partial differential equations.
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►where are the corresponding Cartesian coordinates and , , are constants.
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►Line graphs of the Weierstrass functions , , and , illustrating the lemniscatic and equianharmonic cases.
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►►►Figure 23.4.7:
with , for , = 0.
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►Surfaces for the Weierstrass functions , , and .
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►Figure 23.4.8:
with , for , , .
(The scaling makes the lattice appear to be square.)
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