28.19 Expansions in Series of \mathop{\mathrm{me}_{{\nu+2n}}\/}\nolimits Functions28.21 Graphics

§28.20 Definitions and Basic Properties

Contents

§28.20(i) Modified Mathieu’s Equation

When z is replaced by \pm iz, (28.2.1) becomes the modified Mathieu’s equation:

28.20.1 w^{{\prime\prime}}-\left(a-2q\mathop{\cosh\/}\nolimits\!\left(2z\right)\right)w=0,

with its algebraic form

28.20.2 {(\zeta^{2}-1)w^{{\prime\prime}}+\zeta w^{{\prime}}+\left(4q\zeta^{2}-2q-a\right)w=0}, \zeta=\mathop{\cosh\/}\nolimits z.

§28.20(ii) Solutions \mathop{\mathrm{Ce}_{{\nu}}\/}\nolimits, \mathop{\mathrm{Se}_{{\nu}}\/}\nolimits, \mathop{\mathrm{Me}_{{\nu}}\/}\nolimits, \mathop{\mathrm{Fe}_{{n}}\/}\nolimits, \mathop{\mathrm{Ge}_{{n}}\/}\nolimits

28.20.3 \mathop{\mathrm{Ce}_{{\nu}}\/}\nolimits\!\left(z,q\right)=\mathop{\mathrm{ce}_{{\nu}}\/}\nolimits\!\left(\pm iz,q\right), \nu\neq-1,-2,\dots,
28.20.4 \mathop{\mathrm{Se}_{{\nu}}\/}\nolimits\!\left(z,q\right)=\mp i\mathop{\mathrm{se}_{{\nu}}\/}\nolimits\!\left(\pm iz,q\right), \nu\neq 0,-1,\dots,
28.20.5 \mathop{\mathrm{Me}_{{\nu}}\/}\nolimits\!\left(z,q\right)=\mathop{\mathrm{me}_{{\nu}}\/}\nolimits\!\left(-iz,q\right),
28.20.6 \mathop{\mathrm{Fe}_{{n}}\/}\nolimits\!\left(z,q\right)=\mp i\mathop{\mathrm{fe}_{{n}}\/}\nolimits\!\left(\pm iz,q\right), n=0,1,\dots,
28.20.7 \mathop{\mathrm{Ge}_{{n}}\/}\nolimits\!\left(z,q\right)=\mathop{\mathrm{ge}_{{n}}\/}\nolimits\!\left(\pm iz,q\right), n=1,2,\dots.

§28.20(iii) Solutions \mathop{{\mathrm{M}^{{(j)}}_{{\nu}}}\/}\nolimits

Assume first that \nu is real, q is positive, and a=\mathop{\lambda _{{\nu}}\/}\nolimits\!\left(q\right); see §28.12(i). Write

28.20.8 h=\sqrt{q}\;(>0).

Then from §2.7(ii) it is seen that equation (28.20.2) has independent and unique solutions that are asymptotic to \zeta^{{\ifrac{1}{2}}}e^{{\pm 2ih\zeta}} as \zeta\to\infty in the respective sectors |\mathop{\mathrm{ph}\/}\nolimits\!\left(\mp i\zeta\right)|\leq\tfrac{3}{2}\pi-\delta, \delta being an arbitrary small positive constant. It follows that (28.20.1) has independent and unique solutions \mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right), \mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right) such that

28.20.9 \mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{{H^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(2h\mathop{\cosh\/}\nolimits z\right)\left(1+\mathop{O\/}\nolimits\!\left(\mathop{\mathrm{sech}\/}\nolimits z\right)\right),

as \realpart{z}\to+\infty with -\pi+\delta\leq\imagpart{z}\leq 2\pi-\delta, and

28.20.10 \mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{{H^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(2h\mathop{\cosh\/}\nolimits z\right)\left(1+\mathop{O\/}\nolimits\!\left(\mathop{\mathrm{sech}\/}\nolimits z\right)\right),

as \realpart{z}\to+\infty with -2\pi+\delta\leq\imagpart{z}\leq\pi-\delta. See §10.2(ii) for the notation. In addition, there are unique solutions \mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right), \mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right) that are real when z is real and have the properties

28.20.11 \mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{J_{{\nu}}\/}\nolimits\!\left(2h\mathop{\cosh\/}\nolimits z\right)+e^{{|\imagpart{(2h\mathop{\cosh\/}\nolimits z)}|}}\mathop{O\/}\nolimits\!\left(\left(\mathop{\mathrm{sech}\/}\nolimits z\right)^{{3/2}}\right),
28.20.12 \mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{Y_{{\nu}}\/}\nolimits\!\left(2h\mathop{\cosh\/}\nolimits z\right)+e^{{|\imagpart{(2h\mathop{\cosh\/}\nolimits z)}|}}\mathop{O\/}\nolimits\!\left((\mathop{\mathrm{sech}\/}\nolimits z)^{{3/2}}\right),

as \realpart{z}\to+\infty with |\imagpart{z}|\leq\pi-\delta.

For other values of z, h, and \nu the functions \mathop{{\mathrm{M}^{{(j)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right), j=1,2,3,4, are determined by analytic continuation. Furthermore,

28.20.13 \mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)+i\mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right),
28.20.14 \mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)=\mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)-i\mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right).

§28.20(iv) Radial Mathieu Functions \mathop{{\mathrm{Mc}^{{(j)}}_{{n}}}\/}\nolimits, \mathop{{\mathrm{Ms}^{{(j)}}_{{n}}}\/}\nolimits

For j=1,2,3,4,

28.20.15 \mathop{{\mathrm{Mc}^{{(j)}}_{{n}}}\/}\nolimits\!\left(z,h\right)=\mathop{{\mathrm{M}^{{(j)}}_{{n}}}\/}\nolimits\!\left(z,h\right), n=0,1,\dots,
28.20.16 \mathop{{\mathrm{Ms}^{{(j)}}_{{n}}}\/}\nolimits\!\left(z,h\right)=(-1)^{n}\mathop{{\mathrm{M}^{{(j)}}_{{-n}}}\/}\nolimits\!\left(z,h\right), n=1,2,\dots.

§28.20(v) Solutions \mathop{\mathrm{Ie}_{{n}}\/}\nolimits, \mathop{\mathrm{Io}_{{n}}\/}\nolimits, \mathop{\mathrm{Ke}_{{n}}\/}\nolimits, \mathop{\mathrm{Ko}_{{n}}\/}\nolimits

28.20.17 \mathop{\mathrm{Ie}_{{n}}\/}\nolimits\!\left(z,h\right)=i^{{-n}}\mathop{{\mathrm{Mc}^{{(1)}}_{{n}}}\/}\nolimits\!\left(z,ih\right),
28.20.18 \mathop{\mathrm{Io}_{{n}}\/}\nolimits\!\left(z,h\right)=i^{{-n}}\mathop{{\mathrm{Ms}^{{(1)}}_{{n}}}\/}\nolimits\!\left(z,ih\right),
28.20.19
\mathop{\mathrm{Ke}_{{2m}}\/}\nolimits\!\left(z,h\right)=(-1)^{m}\tfrac{1}{2}\pi i\mathop{{\mathrm{Mc}^{{(3)}}_{{2m}}}\/}\nolimits\!\left(z,ih\right),
\mathop{\mathrm{Ke}_{{2m+1}}\/}\nolimits\!\left(z,h\right)=(-1)^{{m+1}}\tfrac{1}{2}\pi\mathop{{\mathrm{Mc}^{{(3)}}_{{2m+1}}}\/}\nolimits\!\left(z,ih\right),
28.20.20
\mathop{\mathrm{Ko}_{{2m}}\/}\nolimits\!\left(z,h\right)=(-1)^{m}\tfrac{1}{2}\pi i\mathop{{\mathrm{Ms}^{{(3)}}_{{2m}}}\/}\nolimits\!\left(z,ih\right),
\mathop{\mathrm{Ko}_{{2m+1}}\/}\nolimits\!\left(z,h\right)=(-1)^{{m+1}}\tfrac{1}{2}\pi\mathop{{\mathrm{Ms}^{{(3)}}_{{2m+1}}}\/}\nolimits\!\left(z,ih\right).

§28.20(vi) Wronskians

§28.20(vii) Shift of Variable

For n=0,1,2,\dots,

28.20.23
\mathop{{\mathrm{Mc}^{{(j)}}_{{2n}}}\/}\nolimits\!\left(z\pm\tfrac{1}{2}\pi i,h\right)=\mathop{{\mathrm{Mc}^{{(j)}}_{{2n}}}\/}\nolimits\!\left(z,\pm ih\right),
\mathop{{\mathrm{Ms}^{{(j)}}_{{2n+1}}}\/}\nolimits\!\left(z\pm\tfrac{1}{2}\pi i,h\right)=\mathop{{\mathrm{Mc}^{{(j)}}_{{2n+1}}}\/}\nolimits\!\left(z,\pm ih\right),
28.20.24
\mathop{{\mathrm{Mc}^{{(j)}}_{{2n+1}}}\/}\nolimits\!\left(z\pm\tfrac{1}{2}\pi i,h\right)=\mathop{{\mathrm{Ms}^{{(j)}}_{{2n+1}}}\/}\nolimits\!\left(z,\pm ih\right),
\mathop{{\mathrm{Ms}^{{(j)}}_{{2n+2}}}\/}\nolimits\!\left(z\pm\tfrac{1}{2}\pi i,h\right)=\mathop{{\mathrm{Ms}^{{(j)}}_{{2n+2}}}\/}\nolimits\!\left(z,\pm ih\right).

For s\in\Integer,

28.20.25
\mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z+s\pi i,h\right)=e^{{is\pi\nu}}\mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right),
\mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z+s\pi i,h\right)=e^{{-is\pi\nu}}\mathop{{\mathrm{M}^{{(2)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)+2i\mathop{\cot\/}\nolimits\!\left(\pi\nu\right)\mathop{\sin\/}\nolimits\!\left(s\pi\nu\right)\mathop{{\mathrm{M}^{{(1)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right),
\mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z+s\pi i,h\right)=-\dfrac{\mathop{\sin\/}\nolimits\!\left({(s-1)\pi\nu}\right)}{\mathop{\sin\/}\nolimits\!\left(\pi\nu\right)}\mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)-e^{{-i\pi\nu}}\frac{\mathop{\sin\/}\nolimits\!\left(s\pi\nu\right)}{\mathop{\sin\/}\nolimits\!\left(\pi\nu\right)}\mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right),
\mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z+s\pi i,h\right)=e^{{i\pi\nu}}\dfrac{\mathop{\sin\/}\nolimits\!\left(s\pi\nu\right)}{\mathop{\sin\/}\nolimits\!\left(\pi\nu\right)}\mathop{{\mathrm{M}^{{(3)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right)+\frac{\mathop{\sin\/}\nolimits\!\left((s+1)\pi\nu\right)}{\mathop{\sin\/}\nolimits\!\left(\pi\nu\right)}\mathop{{\mathrm{M}^{{(4)}}_{{\nu}}}\/}\nolimits\!\left(z,h\right).

When \nu is an integer the right-hand sides of (28.20.25) are replaced by the their limiting values. And for the corresponding identities for the radial functions use (28.20.15) and (28.20.16).