28 Mathieu Functions and Hill’s EquationModified Mathieu Functions

§28.24 Expansions in Series of Cross-Products of Bessel Functions or Modified Bessel Functions

Throughout this section ε0=2 and εs=1, s=1,2,3,….

With 𝒞μ(j), cnν⁡(q), Anm⁡(q), and Bnm⁡(q) as in §28.23,

28.24.1 c2⁢nν⁡(h2)⁢Mν(j)⁡(z,h)=∑ℓ=−∞∞(−1)ℓ⁢c2⁢ℓν⁡(h2)⁢Jℓ−n⁡(h⁢e−z)⁢𝒞ν+n+ℓ(j)⁡(h⁢ez),

where j=1,2,3,4 and n∈ℤ.

In the case when ν is an integer,

28.24.2 εs⁢Mc2⁢m(j)⁡(z,h) =(−1)m⁢∑ℓ=0∞(−1)ℓ⁢A2⁢ℓ2⁢m⁡(h2)A2⁢s2⁢m⁡(h2)⁢(Jℓ−s⁡(h⁢e−z)⁢𝒞ℓ+s(j)⁡(h⁢ez)+Jℓ+s⁡(h⁢e−z)⁢𝒞ℓ−s(j)⁡(h⁢ez)),
28.24.3 Mc2⁢m+1(j)⁡(z,h) =(−1)m⁢∑ℓ=0∞(−1)ℓ⁢A2⁢ℓ+12⁢m+1⁡(h2)A2⁢s+12⁢m+1⁡(h2)⁢(Jℓ−s⁡(h⁢e−z)⁢𝒞ℓ+s+1(j)⁡(h⁢ez)+Jℓ+s+1⁡(h⁢e−z)⁢𝒞ℓ−s(j)⁡(h⁢ez)),
28.24.4 Ms2⁢m+1(j)⁡(z,h) =(−1)m⁢∑ℓ=0∞(−1)ℓ⁢B2⁢ℓ+12⁢m+1⁡(h2)B2⁢s+12⁢m+1⁡(h2)⁢(Jℓ−s⁡(h⁢e−z)⁢𝒞ℓ+s+1(j)⁡(h⁢ez)−Jℓ+s+1⁡(h⁢e−z)⁢𝒞ℓ−s(j)⁡(h⁢ez)),
28.24.5 Ms2⁢m+2(j)⁡(z,h) =(−1)m⁢∑ℓ=0∞(−1)ℓ⁢B2⁢ℓ+22⁢m+2⁡(h2)B2⁢s+22⁢m+2⁡(h2)⁢(Jℓ−s⁡(h⁢e−z)⁢𝒞ℓ+s+2(j)⁡(h⁢ez)−Jℓ+s+2⁡(h⁢e−z)⁢𝒞ℓ−s(j)⁡(h⁢ez)),

where j=1,2,3,4, and s=0,1,2,….

Also, with In and Kn denoting the modified Bessel functions (§10.25(ii)), and again with s=0,1,2,…,

28.24.6 εs⁢Ie2⁢m⁡(z,h) =(−1)s⁢∑ℓ=0∞(−1)ℓ⁢A2⁢ℓ2⁢m⁡(h2)A2⁢s2⁢m⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Iℓ+s⁡(h⁢ez)+Iℓ+s⁡(h⁢e−z)⁢Iℓ−s⁡(h⁢ez)),
28.24.7 Io2⁢m+2⁡(z,h) =(−1)s⁢∑ℓ=0∞(−1)ℓ⁢B2⁢ℓ+22⁢m+2⁡(h2)B2⁢s+22⁢m+2⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Iℓ+s+2⁡(h⁢ez)−Iℓ+s+2⁡(h⁢e−z)⁢Iℓ−s⁡(h⁢ez)),
28.24.8 Ie2⁢m+1⁡(z,h) =(−1)s⁢∑ℓ=0∞(−1)ℓ⁢B2⁢ℓ+12⁢m+1⁡(h2)B2⁢s+12⁢m+1⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Iℓ+s+1⁡(h⁢ez)+Iℓ+s+1⁡(h⁢e−z)⁢Iℓ−s⁡(h⁢ez)),
28.24.9 Io2⁢m+1⁡(z,h) =(−1)s⁢∑ℓ=0∞(−1)ℓ⁢A2⁢ℓ+12⁢m+1⁡(h2)A2⁢s+12⁢m+1⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Iℓ+s+1⁡(h⁢ez)−Iℓ+s+1⁡(h⁢e−z)⁢Iℓ−s⁡(h⁢ez)),
28.24.10 εs⁢Ke2⁢m⁡(z,h) =∑ℓ=0∞A2⁢ℓ2⁢m⁡(h2)A2⁢s2⁢m⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Kℓ+s⁡(h⁢ez)+Iℓ+s⁡(h⁢e−z)⁢Kℓ−s⁡(h⁢ez)),
28.24.11 Ko2⁢m+2⁡(z,h) =∑ℓ=0∞B2⁢ℓ+22⁢m+2⁡(h2)B2⁢s+22⁢m+2⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Kℓ+s+2⁡(h⁢ez)−Iℓ+s+2⁡(h⁢e−z)⁢Kℓ−s⁡(h⁢ez)),
28.24.12 Ke2⁢m+1⁡(z,h) =∑ℓ=0∞B2⁢ℓ+12⁢m+1⁡(h2)B2⁢s+12⁢m+1⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Kℓ+s+1⁡(h⁢ez)−Iℓ+s+1⁡(h⁢e−z)⁢Kℓ−s⁡(h⁢ez)),
28.24.13 Ko2⁢m+1⁡(z,h) =∑ℓ=0∞A2⁢ℓ+12⁢m+1⁡(h2)A2⁢s+12⁢m+1⁡(h2)⁢(Iℓ−s⁡(h⁢e−z)⁢Kℓ+s+1⁡(h⁢ez)+Iℓ+s+1⁡(h⁢e−z)⁢Kℓ−s⁡(h⁢ez)).

The expansions (28.24.1)–(28.24.13) converge absolutely and uniformly on compact sets of the z-plane.

For further power series of Mathieu radial functions of integer order for small parameters and improved convergence rate see Larsen et al. (2009).