§30.11 Radial Spheroidal Wave Functions
Contents
§30.11(i) Definitions
§30.11(ii) Graphics
§30.11(iii) Asymptotic Behavior
§30.11(iv) Wronskian
§30.11(v) Connection with the 𝑃𝑠 and 𝑄𝑠
Functions
§30.11(vi) Integral Representations
§30.11(i) Definitions
Denote
30.11.1
ψ k ( j ) ( z ) = ( π 2 z ) 1 2 𝒞 k + 1 2 ( j ) ( z ) ,
j = 1 , 2 , 3 , 4 ,
where
30.11.2
𝒞 ν ( 1 )
= J ν ,
𝒞 ν ( 2 )
= Y ν ,
𝒞 ν ( 3 )
= H ν ( 1 ) ,
𝒞 ν ( 4 )
= H ν ( 2 ) ,
with J ν , Y ν , H ν ( 1 ) , and
H ν ( 2 ) as in §10.2(ii) . Then solutions of
(30.2.1 ) with μ = m and
λ = λ n m ( γ 2 ) are given by
30.11.3
S n m ( j ) ( z , γ ) = ( 1 − z − 2 ) 1 2 m A n − m ( γ 2 ) ∑ 2 k ≥ m − n a n , k − m ( γ 2 ) ψ n + 2 k ( j ) ( γ z ) .
Here a n , k − m ( γ 2 ) is defined by (30.8.2 ) and
(30.8.6 ), and
30.11.4
A n ± m ( γ 2 ) = ∑ 2 k ≥ ∓ m − n ( − 1 ) k a n , k ± m ( γ 2 ) ( ≠ 0 ) .
In (30.11.3 ) z ≠ 0 when j = 1 , and | z | > 1 when j = 2 , 3 , 4 .
Connection Formulas
30.11.5
S n m ( 3 ) ( z , γ )
= S n m ( 1 ) ( z , γ ) + i S n m ( 2 ) ( z , γ ) ,
S n m ( 4 ) ( z , γ )
= S n m ( 1 ) ( z , γ ) − i S n m ( 2 ) ( z , γ ) .
§30.11(ii) Graphics
Figure 30.11.1: S n 0 ( 1 ) ( x , 2 ) ,
n = 0 , 1 , 1 ≤ x ≤ 10 .
Magnify
Figure 30.11.2: S n 0 ( 1 ) ( i y , 2 i ) ,
n = 0 , 1 , 0 ≤ y ≤ 10 .
Magnify
Figure 30.11.3: S n 1 ( 1 ) ( x , 2 ) ,
n = 1 , 2 , 1 ≤ x ≤ 10 .
Magnify
Figure 30.11.4: S n 1 ( 1 ) ( i y , 2 i ) ,
n = 1 , 2 , 0 ≤ y ≤ 10 .
Magnify
§30.11(iii) Asymptotic Behavior
For fixed γ , as z → ∞
in the sector | ph z | ≤ π − δ (< π ),
30.11.6
S n m ( j ) ( z , γ ) = { ψ n ( j ) ( γ z ) + O ( z − 2 e | ℑ z | ) , j = 1 , 2 , ψ n ( j ) ( γ z ) ( 1 + O ( z − 1 ) ) , j = 3 , 4 .
For asymptotic expansions in negative powers of z see
Meixner and Schäfke (1954 , p. 293) .
§30.11(iv) Wronskian
30.11.7
𝒲 { S n m ( 1 ) ( z , γ ) , S n m ( 2 ) ( z , γ ) } = 1 γ ( z 2 − 1 ) .
§30.11(v) Connection with the 𝑃𝑠 and 𝑄𝑠
Functions
30.11.8
S n m ( 1 ) ( z , γ ) = K n m ( γ ) 𝑃𝑠 n m ( z , γ 2 ) ,
30.11.9
S n m ( 2 ) ( z , γ ) = ( n − m ) ! ( n + m ) ! ( − 1 ) m + 1 𝑄𝑠 n m ( z , γ 2 ) γ K n m ( γ ) A n m ( γ 2 ) A n − m ( γ 2 ) ,
where
30.11.10
K n m ( γ ) = π 2 ( γ 2 ) m ( − 1 ) m a n , 1 2 ( m − n ) − m ( γ 2 ) Γ ( 3 2 + m ) A n − m ( γ 2 ) 𝖯𝗌 n m ( 0 , γ 2 ) ,
n − m even,
or
30.11.11
K n m ( γ ) = π 2 ( γ 2 ) m + 1 ( − 1 ) m a n , 1 2 ( m − n + 1 ) − m ( γ 2 ) Γ ( 5 2 + m ) A n − m ( γ 2 ) ( d 𝖯𝗌 n m ( z , γ 2 ) / d z | z = 0 ) ,
n − m odd.
§30.11(vi) Integral Representations
When z ∈ ℂ ∖ ( − ∞ , 1 ]
30.11.12
A n − m ( γ 2 ) S n m ( 1 ) ( z , γ ) = 1 2 i m + n γ m ( n − m ) ! ( n + m ) ! z m ( 1 − z − 2 ) 1 2 m ∫ − 1 1 e − i γ z t ( 1 − t 2 ) 1 2 m 𝖯𝗌 n m ( t , γ 2 ) d t .
For further relations see Arscott (1964b , §8.6) ,
Connett et al. (1993 ) , Erdélyi et al. (1955 , §16.13) ,
Meixner and Schäfke (1954 ) , and Meixner et al. (1980 , §3.1) .
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