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►When the path of integration excludes the origin and does not cross the negative real axis (8.19.2) defines the principal value of , and unless indicated otherwise in the DLMF principal values are assumed.
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►In Figures 8.19.2–8.19.5, height corresponds to the absolute value of the function and color to the phase.
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►The principal branch of corresponds to the principal value of (§4.2(iv)) and is analytic in the -plane cut along the interval .
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►Except in the case of , the principal branches of and are two-valued and discontinuous on the cut
; compare §4.2(i).
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►The principal branches correspond to principal values of the square roots in (10.2.5) and (10.2.6), again with a cut in the -plane along the interval .
►The principal branches of and are two-valued and discontinuous on the cut
.
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►Other notations and names for include (Kölbig et al. (1970)), Spence function (’t Hooft and Veltman (1979)), and (Maximon (2003)).
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►The principal branch has a cut along the interval and agrees with (25.12.1) when ; see also §4.2(i).
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►Figure 25.12.2: Absolute value of the dilogarithm function , , .
Principal value.
There is a cut along the real axis from 1 to .
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►For other values of , is defined by analytic continuation.
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►Figure 19.3.9:
as a function of complex for , .
…On the branch cut () it is infinite at , and has the value
when .
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►Figure 19.3.10:
as a function of complex for , .
…On the upper edge of the branch cut () it has the value
if , and if .
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►Figure 19.3.11:
as a function of complex for , .
…On the branch cut () it has the value
, with limit 1 as .
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►Figure 19.3.12:
as a function of complex for , .
…On the upper edge of the branch cut () it has the (negative) value
, with limit 0 as .
Magnify3DHelp
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►The surface color map can be changed from height-based to phase-based for complex valued functions, and density plots can be generated through strategic scaling.
Moreover, a cutting plane feature allows users to track curves of intersection produced as a moving plane cuts through the function surface.
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