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22 Jacobian Elliptic FunctionsProperties

§22.10 Maclaurin Series

Contents
  1. §22.10(i) Maclaurin Series in z
  2. §22.10(ii) Maclaurin Series in k and k

§22.10(i) Maclaurin Series in z

Initial terms are given by

22.10.1 sn(z,k)=z(1 k2)z33! (1 14k2 k4)z55!(1 135k2 135k4 k6)z77! O(z9),
22.10.2 cn(z,k)=1z22! (1 4k2)z44!(1 44k2 16k4)z66! O(z8),
22.10.3 dn(z,k)=1k2z22! k2(4 k2)z44!k2(16 44k2 k4)z66! O(z8).

Further terms may be derived by substituting in the differential equations (22.13.13), (22.13.14), (22.13.15). The full expansions converge when |z|<min(K(k),K(k)).

§22.10(ii) Maclaurin Series in k and k

Initial terms are given by

22.10.4 sn(z,k)=sinzk24(zsinzcosz)cosz O(k4),
22.10.5 cn(z,k)=cosz k24(zsinzcosz)sinz O(k4),
22.10.6 dn(z,k)=1k22sin2z O(k4),
22.10.7 sn(z,k)=tanhzk24(zsinhzcoshz)sech2z O(k4),
22.10.8 cn(z,k)=sechz k24(zsinhzcoshz)tanhzsechz O(k4),
22.10.9 dn(z,k)=sechz k24(z sinhzcoshz)tanhzsechz O(k4).

Further terms may be derived from the differential equations (22.13.13), (22.13.14), (22.13.15), or from the integral representations of the inverse functions in §22.15(ii). The radius of convergence is the distance to the origin from the nearest pole in the complex k-plane in the case of (22.10.4)–(22.10.6), or complex k-plane in the case of (22.10.7)–(22.10.9); see §22.17.