►A lattice path is a directed path on the plane integer lattice .
…For an example see Figure 26.9.2.
►A k-dimensional lattice path is a directed path composed of segments that connect vertices in so that each segment increases one coordinate by exactly one unit.
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►Care needs to be taken to choose integration paths in such a way that the wanted solution is growing in magnitude along the path at least as rapidly as all other solutions (§3.7(ii)).
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►The integration path begins at , encircles once in the positive sense, followed by once in the positive sense, and so on, returning finally to .
The integration path is called a Pochhammer double-loop
contour (compare Figure 5.12.3).
The branches of the many-valued functions are continuous on the path, and assume their principal values at the beginning.
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►and the integration paths
, are Pochhammer double-loop contours encircling distinct pairs of singularities , , .
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►For bi-orthogonal relations for path-multiplicative solutions see Schmidt (1979, §2.2).
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►It follows that also equals the number of partitions of into parts that are less than or equal to .
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►It is also equal to the number of lattice paths from to that have exactly vertices , , , above and to the left of the lattice path.
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►Figure 26.9.2: The partition represented as a lattice path.
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►As described in §3.7(ii), to ensure stability the integration path must be chosen in such a way that as we proceed along it the wanted solution grows at least as fast as all other solutions of the differential equation.
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►In the first method the integration path for the contour integral (9.5.4) is deformed to coincide with paths of steepest descent (§2.4(iv)).
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