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►Formal -periodic solutions can be constructed as Fourier series; compare §28.4:
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►where when , and when .
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►For , the functions , behave asymptotically as multiples of as .
All other periodic solutions behave as multiples of .
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►All other periodic solutions behave as multiples of .
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►The functions , , provide periodic solutions of the partial differential equation
…with .
►For , with real, (20.13.1) takes the form of a real-time diffusion equation
…Thus the classical theta functions are “periodized”, or “anti-periodized”, Gaussians; see Bellman (1961, pp. 18, 19).
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►In the singular limit , the functions , , become integral kernels of Feynman path integrals (distribution-valued Green’s functions); see Schulman (1981, pp. 194–195).
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►Figure 21.4.2:
, , .
(The imaginary part looks very similar.)
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►Figure 21.4.4: A real-valued scaled Riemann theta function: , , .
In this case, the quasi-periods are commensurable, resulting in a doubly-periodic configuration.
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