§13.4 Integral Representations
Contents
§13.4(i) Integrals Along the Real Line
§13.4(ii) Contour Integrals
§13.4(iii) Mellin–Barnes Integrals
§13.4(i) Integrals Along the Real Line
13.4.1
𝐌 ( a , b , z ) = 1 Γ ( a ) Γ ( b − a ) ∫ 0 1 e z t t a − 1 ( 1 − t ) b − a − 1 d t ,
ℜ b > ℜ a > 0 ,
13.4.2
𝐌 ( a , b , z ) = 1 Γ ( b − c ) ∫ 0 1 𝐌 ( a , c , z t ) t c − 1 ( 1 − t ) b − c − 1 d t ,
ℜ b > ℜ c > 0 ,
13.4.3
𝐌 ( a , b , − z ) = z 1 2 − 1 2 b Γ ( a ) ∫ 0 ∞ e − t t a − 1 2 b − 1 2 J b − 1 ( 2 z t ) d t ,
ℜ a > 0 .
For the function J b − 1 see §10.2(ii) .
13.4.4
U ( a , b , z ) = 1 Γ ( a ) ∫ 0 ∞ e − z t t a − 1 ( 1 + t ) b − a − 1 d t ,
ℜ a > 0 , | ph z | < 1 2 π ,
13.4.5
U ( a , b , z ) = z 1 − a Γ ( a ) Γ ( 1 + a − b ) ∫ 0 ∞ U ( b − a , b , t ) e − t t a − 1 t + z d t ,
| ph z | < π , ℜ a > max ( ℜ b − 1 , 0 ) ,
13.4.6
U ( a , b , z ) = ( − 1 ) n z 1 − b − n Γ ( 1 + a − b ) ∫ 0 ∞ 𝐌 ( b − a , b , t ) e − t t b + n − 1 t + z d t ,
| ph z | < π ,
n = 0 , 1 , 2 , … ,
− ℜ b < n < 1 + ℜ ( a − b ) ,
13.4.7
U ( a , b , z ) = 2 z 1 2 − 1 2 b Γ ( a ) Γ ( a − b + 1 ) ∫ 0 ∞ e − t t a − 1 2 b − 1 2 K b − 1 ( 2 z t ) d t ,
ℜ a > max ( ℜ b − 1 , 0 ) ,
13.4.8
U ( a , b , z ) = z c − a ∫ 0 ∞ e − z t t c − 1 𝐅 1 2 ( a , a − b + 1 ; c ; − t ) d t ,
| ph z | < 1 2 π ,
where c is arbitrary,
ℜ c > 0 . For the functions K b − 1 and 𝐅 1 2
see §10.25(ii) and §§15.1 , 15.2(i) .
§13.4(ii) Contour Integrals
13.4.9
𝐌 ( a , b , z ) = Γ ( 1 + a − b ) 2 π i Γ ( a ) ∫ 0 ( 1 + ) e z t t a − 1 ( t − 1 ) b − a − 1 d t ,
b − a ≠ 1 , 2 , 3 , … , ℜ a > 0 .
13.4.10
𝐌 ( a , b , z ) = e − a π i Γ ( 1 − a ) 2 π i Γ ( b − a ) ∫ 1 ( 0 + ) e z t t a − 1 ( 1 − t ) b − a − 1 d t ,
a ≠ 1 , 2 , 3 , … , ℜ ( b − a ) > 0 .
Figure 13.4.1: Contour of integration in (13.4.11 ).
(Compare Figure 5.12.3 .)
Magnify
13.4.11
𝐌 ( a , b , z ) = e − b π i Γ ( 1 − a ) Γ ( 1 + a − b ) 1 4 π 2 × ∫ α ( 0 + , 1 + , 0 − , 1 − ) e z t t a − 1 ( 1 − t ) b − a − 1 d t ,
a , b − a ≠ 1 , 2 , 3 , … .
The contour of integration starts and terminates at a point α
on the real axis between
0 and 1 . It encircles t = 0 and t = 1 once in the positive sense,
and then once in the negative sense. See Figure 13.4.1 . The fractional
powers are continuous and assume their principal values at t = α .
Similar conventions also apply to the remaining integrals in this subsection.
13.4.12
𝐌 ( a , c , z ) = Γ ( b ) 2 π i z 1 − b ∫ − ∞ ( 0 + , 1 + ) e z t t − b 𝐅 1 2 ( a , b ; c ; 1 / t ) d t ,
b ≠ 0 , − 1 , − 2 , … , | ph z | < 1 2 π .
At the point where the contour crosses the interval ( 1 , ∞ ) , t − b and
the 𝐅 1 2 function assume their principal values; compare
§§15.1 and 15.2(i) . A special case is
13.4.13
𝐌 ( a , b , z ) = z 1 − b 2 π i ∫ − ∞ ( 0 + , 1 + ) e z t t − b ( 1 − 1 t ) − a d t ,
| ph z | < 1 2 π .
13.4.14
U ( a , b , z ) = e − a π i Γ ( 1 − a ) 2 π i ∫ ∞ ( 0 + ) e − z t t a − 1 ( 1 + t ) b − a − 1 d t ,
a ≠ 1 , 2 , 3 , … , | ph z | < 1 2 π .
The contour cuts the real axis between − 1 and 0 . At this
point the fractional powers are determined by
ph t = π and ph ( 1 + t ) = 0 .
13.4.15
U ( a , b , z ) Γ ( c ) Γ ( c − b + 1 ) = z 1 − c 2 π i ∫ − ∞ ( 0 + ) e z t t − c 𝐅 1 2 ( a , c ; a + c − b + 1 ; 1 − 1 t ) d t ,
| ph z | < 1 2 π .
Again, t − c and the 𝐅 1 2 function assume their principal values where the
contour (see Figure 5.9.1 ) intersects the positive real axis.
§13.4(iii) Mellin–Barnes Integrals
If a ≠ 0 , − 1 , − 2 , … , then
13.4.16
𝐌 ( a , b , − z ) = 1 2 π i Γ ( a ) ∫ − i ∞ i ∞ Γ ( a + t ) Γ ( − t ) Γ ( b + t ) z t d t ,
| ph z | < 1 2 π ,
where the contour of integration separates the poles of
Γ ( a + t ) from those of Γ ( − t ) .
If a and a − b + 1 ≠ 0 , − 1 , − 2 , … , then
13.4.17
U ( a , b , z ) = z − a 2 π i ∫ − i ∞ i ∞ Γ ( a + t ) Γ ( 1 + a − b + t ) Γ ( − t ) Γ ( a ) Γ ( 1 + a − b ) z − t d t ,
| ph z | < 3 2 π ,
where the contour of integration separates the poles of
Γ ( a + t ) Γ ( 1 + a − b + t ) from those of Γ ( − t ) .
13.4.18
U ( a , b , z ) = z 1 − b e z 2 π i ∫ − i ∞ i ∞ Γ ( b − 1 + t ) Γ ( t ) Γ ( a + t ) z − t d t ,
| ph z | < 1 2 π ,
where the contour of integration passes all the poles of
Γ ( b − 1 + t ) Γ ( t ) on the right-hand side.
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