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DLMF: §19.20 Special Cases ‣ Symmetric Integrals ‣ Chapter 19 Elliptic Integrals
§19.20 Special Cases
Contents
§19.20(i) R F ( x , y , z )
§19.20(ii) R G ( x , y , z )
§19.20(iii) R J ( x , y , z , p )
§19.20(iv) R D ( x , y , z )
§19.20(v) R − a ( 𝐛 ; 𝐳 )
§19.20(i) R F ( x , y , z )
In this subsection, and also §§19.20(ii) –19.20(v) , the
variables of all R -functions satisfy the constraints specified in
§19.16(i) unless other conditions are stated.
19.20.1
R F ( x , x , x )
= x − 1 / 2 ,
R F ( λ x , λ y , λ z )
= λ − 1 / 2 R F ( x , y , z ) ,
R F ( x , y , y )
= R C ( x , y ) ,
R F ( 0 , y , y )
= 1 2 π y − 1 / 2 ,
R F ( 0 , 0 , z )
= ∞ .
The first lemniscate constant is given by
19.20.2
∫ 0 1 d t 1 − t 4 = R F ( 0 , 1 , 2 ) = ( Γ ( 1 4 ) ) 2 4 ( 2 π ) 1 / 2 = 1.31102 87771 46059 90523 … .
Todd (1975 ) refers to a proof by T. Schneider that this is a
transcendental number. The general lemniscatic case is
19.20.3
R F ( x , a , y ) = R − 1 4 ( 3 4 , 1 2 ; a 2 , x y ) ,
a = 1 2 ( x + y ) .
§19.20(ii) R G ( x , y , z )
19.20.4
R G ( x , x , x )
= x 1 / 2 ,
R G ( λ x , λ y , λ z )
= λ 1 / 2 R G ( x , y , z ) ,
R G ( 0 , y , y )
= 1 4 π y 1 / 2 ,
R G ( 0 , 0 , z )
= 1 2 z 1 / 2 ,
19.20.5
2 R G ( x , y , y ) = y R C ( x , y ) + x .
§19.20(iii) R J ( x , y , z , p )
19.20.6
R J ( x , x , x , x )
= x − 3 / 2 ,
R J ( λ x , λ y , λ z , λ p )
= λ − 3 / 2 R J ( x , y , z , p ) ,
R J ( x , y , z , z )
= R D ( x , y , z ) ,
R J ( 0 , 0 , z , p )
= ∞ ,
R J ( x , x , x , p )
= R D ( p , p , x ) = 3 x − p ( R C ( x , p ) − 1 x ) ,
x ≠ p , x p ≠ 0 .
19.20.7
R J ( x , y , z , p ) → + ∞ ,
p → 0 + or 0 − ; x , y , z > 0 .
19.20.8
R J ( 0 , y , y , p )
= 3 π 2 ( y p + p y ) ,
p > 0 ,
R J ( 0 , y , y , − q )
= − 3 π 2 y ( y + q ) ,
q > 0 ,
R J ( x , y , y , p )
= 3 p − y ( R C ( x , y ) − R C ( x , p ) ) ,
p ≠ y ,
R J ( x , y , y , y )
= R D ( x , y , y ) .
19.20.9
R J ( 0 , y , z , ± y z ) = ± 3 2 y z R F ( 0 , y , z ) .
19.20.10
lim p → 0 + p R J ( 0 , y , z , p )
= 3 π 2 y z ,
lim p → 0 − R J ( 0 , y , z , p )
= − R D ( 0 , y , z ) − R D ( 0 , z , y ) = − 6 y z R G ( 0 , y , z ) .
19.20.11
R J ( 0 , y , z , p ) = 3 2 p z ln ( 16 z y ) − 3 p R C ( z , p ) + O ( y ln y ) ,
y → 0 + ; p (≠ 0 ) real.
19.20.12
lim p → ± ∞ p R J ( x , y , z , p ) = 3 R F ( x , y , z ) .
19.20.13
2 ( p − x ) R J ( x , y , z , p ) = 3 R F ( x , y , z ) − 3 x R C ( y z , p 2 ) ,
p = x ± ( y − x ) ( z − x ) ,
where x , y , z may be permuted.
When the variables are real and distinct, the various cases of
R J ( x , y , z , p ) are called circular (hyperbolic) cases if
( p − x ) ( p − y ) ( p − z ) is positive (negative), because they typically occur in
conjunction with inverse circular (hyperbolic) functions. Cases encountered in
dynamical problems are usually circular; hyperbolic cases include Cauchy
principal values. If x , y , z are permuted so that 0 ≤ x < y < z , then the
Cauchy principal value of R J is given by
19.20.14
( q + z ) R J ( x , y , z , − q ) = ( p − z ) R J ( x , y , z , p ) − 3 R F ( x , y , z ) + 3 ( x y z x y + p q ) 1 / 2 R C ( x y + p q , p q ) ,
valid when
19.20.15
q
> 0 ,
p
= z ( x + y + q ) − x y z + q ,
or
19.20.16
p
= w y + ( 1 − w ) z ,
w
= z − x z + q ,
0
< w < 1 .
Since x < y < p < z , p is in a hyperbolic region. In the complete case
(x = 0 ) (19.20.14 ) reduces to
19.20.17
( q + z ) R J ( 0 , y , z , − q ) = ( p − z ) R J ( 0 , y , z , p ) − 3 R F ( 0 , y , z ) ,
p = z ( y + q ) / ( z + q ) , w = z / ( z + q ) .
§19.20(iv) R D ( x , y , z )
19.20.18
R D ( x , x , x )
= x − 3 / 2 ,
R D ( λ x , λ y , λ z )
= λ − 3 / 2 R D ( x , y , z ) ,
R D ( 0 , y , y )
= 3 4 π y − 3 / 2 ,
R D ( 0 , 0 , z )
= ∞ .
19.20.19
R D ( x , y , z ) ∼ 3 x − 1 / 2 y − 1 / 2 z − 1 / 2 ,
z / x y → 0 .
19.20.20
R D ( x , y , y ) = 3 2 ( y − x ) ( R C ( x , y ) − x y ) ,
x ≠ y , y ≠ 0 ,
19.20.21
R D ( x , x , z ) = 3 z − x ( R C ( z , x ) − 1 z ) ,
x ≠ z , x z ≠ 0 .
The second lemniscate constant is given by
19.20.22
∫ 0 1 t 2 d t 1 − t 4 = 1 3 R D ( 0 , 2 , 1 ) = ( Γ ( 3 4 ) ) 2 ( 2 π ) 1 / 2 = 0.59907 01173 67796 10371 … .
Todd (1975 ) refers to a proof by T. Schneider that this is a
transcendental number. Compare (19.20.2 ). The general
lemniscatic case is
19.20.23
R D ( x , y , a ) = R − 3 4 ( 5 4 , 1 2 ; a 2 , x y ) ,
a = 1 2 x + 1 2 y .
§19.20(v) R − a ( 𝐛 ; 𝐳 )
Define c = ∑ j = 1 n b j . Then
19.20.24
R 0 ( 𝐛 ; 𝐳 )
= 1 ,
R N ( 𝐛 ; 𝐳 )
= N ! ( c ) N T N ( 𝐛 , 𝐳 ) ,
N = 0 , 1 , 2 , … ,
where T N is defined by (19.19.1 ). Also,
19.20.25
R − c ( 𝐛 ; 𝐳 ) = ∏ j = 1 n z j − b j ,
19.20.26
R − a ( 𝐛 ; 𝐳 ) = ∏ j = 1 n z j − b j R − a ′ ( 𝐛 ; 𝒛 − 𝟏 ) ,
a + a ′ = c , 𝒛 − 𝟏 = ( z 1 − 1 , … , z n − 1 ) .
See also (19.16.11 ) and (19.16.19 ).