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Analysis of the Parareal Time-Parallel Time-Integration method

GANDER, Martin Jakob, VANDEWALLE, Stefan

Abstract

The parareal algorithm is a method to solve time-dependent problems parallel in time: it approximates parts of the solution later in time simultaneously to parts of the solution earlier in time. In this paper the relation of the parareal algorithm to space-time multigrid and multiple shooting methods is first briefly discussed. The focus of the paper is on new convergence results that show superlinear convergence of the algorithm when used on bounded time intervals, and linear convergence for unbounded intervals.

GANDER, Martin Jakob, VANDEWALLE, Stefan. Analysis of the Parareal Time-Parallel Time-Integration method. SIAM Journal on Scientific Computing , 2007, vol. 29, no. 2, p.

556-578

Available at:

http://archive-ouverte.unige.ch/unige:6312

Disclaimer: layout of this document may differ from the published version.

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-/L"%JIV K L. GUKML&bN2 & IK  & IT=VJI 8}=N( V E}mKKsG=ƒ

0 1 1 4

")( ƒ 0 = 1 4

Q

! V V GW~" & ! G=fG=ƒ ! KGUT=VJ~BG=NUT 08IV$ GWLNfVJƒ]G 9fGJIGW~~VJ~6LNmKsV (;IGUK L&bN

$ V K #&=T<(\&WIf" &b~GJIf"s#"KV$?Th=NJGW$ L%S" ƒ @?(?h€

(31)

−50 0 50 100

−60

−40

−20 0 20 40 60

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(32)

−2 −1 0 1 2

−1.5

−1

−0.5 0 0.5 1 1.5

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(33)

−1.5 −1 −0.5 0 0.5 1

−1.5

−1

−0.5 0 0.5 1 1.5

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(34)

−1.5 −1 −0.5 0 0.5 1

−1.5

−1

−0.5 0 0.5 1 1.5

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(35)

−1.5 −1 −0.5 0 0.5 1

−1.5

−1

−0.5 0 0.5 1 1.5

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(36)

−1.5 −1 −0.5 0 0.5 1

−1.5

−1

−0.5 0 0.5 1 1.5

x1

x2

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

t

x

(37)

)69 ˆ<f9 ‚-) <bAC):-)) 3 0S<B%"-/3g9

1 B =

= 1 "NB c

=

" 1 A=

T "

0 10

20 30

40 50

−20

−15

−10

−5 0 5 10 15 20

−40

−20 0 20 40

!@GJIGW$ V KVJI"A2

1 …BƒCc1 „ G=NUT T1 1 /

%JJG-&JK L% IV (bLg$ VhQ

NWLK LG=~%,&bNUT@LK L&bN-"A2 5 = "27 5 …71@5 „h… '

'7

! L$ }=~GUKML&bN K Lg$ V2

= #…

1 1 …

-/L"%JIV K L. GUKML&bN2 &b}WIK  & IT=VJI 8}WN ( V E}mKKsG=ƒ

0 1 1 4

ƒ 0 = 1 4

Q

(38)

0 1 2 3 4 5 6 7 8 9 10

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(39)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(40)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(41)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(42)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(43)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(44)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(45)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(46)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(47)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(48)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(49)

0 1 2 3 4 5 6 7 8 9 10

−20

−10 0 10 20 30 40

t

x

0 1 2 3 4 5 6 7 8 9 10

10 −15 10 −10 10 −5 10 0

t

x

(50)

0 2 4 6 8 10 12 10 −10

10 −8 10 −6 10 −4 10 −2 10 0 10 2

Error, L2 in x, Linf in t

iteration

(51)

' ) %"5S0 ) 78)f %('*) 3S<U9 -) P+ 9 + )fs9&) 0S<B%"-/3

.

BD.8. 1 C. L"N 1 #…

.5 M…7 1 " LN85 „ 7

> L"%,&" LK( <1

(

ƒC#&$%&)( VJNUV,&b}-" &b}=NUTBGJI %,&bNUT;LKML&bN:"

9CVJNmKsVJIV T *gN LKsV T;L*gVJIVJN % V T@L"%JIV K L. GUK L&bNWƒ

0 1

(

G% * GJITS}W~VJI LN KML$ VJƒ

0 1 1

ƒ 0 = 1

Q

0 0.2

0.4 0.6

0.8

1 0

0.05 0.1

−1

−0.5 0 0.5 1

t x

solution

(52)

+ )fs9&) 0S<B%"-/3 56-/3 )f+ ) 3C5]) :):A 0 %"-)

0 5 10 15

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0

iteration

error

T=4, 400 proc

T=1, 100 proc

T=0.25, 25 proc

T=0.17, 17 proc

T=0.1, 10 proc

(53)

-/3 )f+ ) 3C5]) -) <BAC) )]0S< 0S<=%-/3

1

:8X

O a ca cdX

a V a V P cdM

= : ` a[OWO VUMgX

Y =P =

:8X :8X

a8=

X A.

a=

M

P]b

. 1 0 .

Y MKS^,cdX

=M"X Y j M= :

a]b

?K

=da T8VgX

` X = : PAY

Mb =M` X ^

P]b

X,c X K%K[.

O

X,cdVgM

b X a cdV=

P]b T P .

bWY

X Y =M` X M

b=

X,c

a VK6e

$ G )

.

.5

=5.

7 '

. "

i

5 -

7 $ G )

.

.5

=5.

7 ' . "

j

:8X,cdX

=

:8X/^

P]b

K

=dab=

MK . b M

X,cK

a V 3P c X a

^<: ?K

=da T8VgX

` X =: PAY

@

- b . b T P .

bWY

X Y =M` X M

b=

X,c

a VK =

:8X ^

P]b X,c X b

^,XMKNVUM

b X a ce

" }89

.

.5

=5.

7 '

. "

" }89

.

.25

=/.

7 '

. "

j

:8X,cdX

ZMK . b M

X,cK a V 3P c X a

^<: ?K

=a T8VgX

` X = : PAY

@

(54)

-/3 )f+ ) 3C5]) - 3g9J<h0 3S<U9 - <bAC) )S0S< 0S<B%"-/3

$ V K #&=T & ITWVJI

…bQˆ„h… h† h„A …bQˆ„(?BAW„'h†h…h€'

! - bQ …bQ € €(?BA „h„h… …bQˆ„ @?Ah€

! - bQˆ„ …bQˆ„h…h€ h„h„h„h†h€ …bQ €Ah… h€h†h€

CGfT=G=} Z; ' …bQˆ…h† BA'(?h„h†'h… …bQˆ…h†h€h€'(?h„ †'

&JKsV K‚fGUK WL(;UVJI>& IT=VJI:K Lg$ VPLNUKV (;IGUK L&bN $ V K‚-&BT" ~V GUT K &Z({G-"KsVJI

%,&bNfVJI&( VJN% V&#( K‚UV 9fGhIGJIV G=~;GW~(& I{LK W$ K‚fG=N ~&3* VJI & IT=VJI $ V K #&=T8" Q

(55)

-/3 )f+ ) 3C5]) -).7 ) D )65@<=%-/3 - ):' 9

1

:8X

O a ca cdX

a V a V P cdM

= : ` a[OWO VUMgX

Y =P =

:8X

a]Y X,^

= M P]b

X .

a8=

M

P]b .

1@.

j M= :<T

a

^,i

jCa

c Y .]VgX,c Mb = M` X ^

P]b

X,c X K%K[.

O

X,cdVgM

b X a cdV=

P]b T P .

b8Y X Y

= M` X M b=

X,c

Sa VK6e

$ G )

.

.25

=/.

7 '

. "

i

5 - 7 $ G )

.

.5

=/.

7 '

. "

j

:8X,cdX

=

:8X/^

P]b

K

=dab=

MK . b M

X,cK

a

VLe

1 )5#„h„BA ' BAW„h†@

( 1

>&,%,&bNfVJI( VJN % V IVS" }W~K (& I }WN&b}WNUT=V T K Lg$ VPLNmKsVJIhGW~" Q

; " " &W&bN G-" $%& IV K‚fG=N- LKsVJIGUKML&bN:" GJIV NUV V TWV T6ƒ@K‚UVZ$ V K #&=T

~&A&"lVS" G=~#~;L"NmKsVJIVS"K‚Q

(56)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(57)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(58)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(59)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(60)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(61)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(62)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.4

−0.2 0 0.2 0.4

x t

error

(63)

0 1 2 3 4 0

0.5 1

1.5 0 0.5 1

x t

u

0 1 2 3 4

0 0.5

1 1.5

−0.2 0 0.2

x t

error

(64)

0 1 2 3 4 5 6 7 8 10 −16

10 −14 10 −12 10 −10 10 −8 10 −6 10 −4 10 −2 10 0 10 2 10 4

iteration

Error

Superlinear bound

(65)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−0.5 0 0.5 1

x t

error

(66)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−0.2 0 0.2

x t

error

(67)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−0.05 0 0.05

x t

error

(68)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−0.02 0 0.02

x t

error

(69)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−4

−2 0 2

x 10 −3

x t

error

(70)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4 0 5 10

x 10 −4

x t

error

(71)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−2

−1 0 1

x 10 −4

x t

error

(72)

0 1 2 3 4 0.1 0

0.3 0.2 0.5 −1 0.4

0 1

x t

u

0 1 2 3 4

0.1 0 0.3 0.2

0.5 0.4

−3

−2

−1 0 1

x 10 −5

x t

error

(73)

0 1 2 3 4 5 6 7 8 10 −6

10 −5 10 −4 10 −3 10 −2 10 −1 10 0 10 1 10 2 10 3 10 4

iteration

Error

Superlinear bound

(74)

<BAC) . 7 7 %5]0g<=%- 3g9 0 3CD )@9 #<U9 -/34 0 l0f)S0

,! €*+T &/ = T 1 9 & IK LG=~ƒ JGhI!fGUK‚ƒ 98JG=NUTWVS" I!L" 5„h…h… Bƒ

„h…h…h†7

8$8 <7 $d7

"

/( 1 FHGfT=G‚ ƒ

!

G=~&$ &bNWƒ 08}=I{LNWL%fL

5„h…h…h„Bƒg„h…h…h†7

3**+

"

*‹7T *T8$ 1 R2GJI!I{LT8&bƒ A",9 V T=G=~#ƒ 6~GfT $ GJI 5 „h…h… Bƒ

„h…h…'7

*T% "

& I 1 @L"%JUVJIƒ$2V3%JmK‚ƒ:FHGfT=G‚ 5 „h…h… 7

"  1*+4*q/ 1$ /(*4 1 ! KG[* G=NUTbN#+@} L"K%5 „h…h… 7

8T 7T 0 /$ * € 1 G %,&bƒ VJI!NfGJIT@ƒ FHGfT=G‚ ƒ 08}=I{LNWL%fLƒ

gVJIG=<5 „h…h…h„7

*+$ $ B 1 G=~ƒCFHGfTBG‚ 5 „h…h…h„7

)')T *T "

#

'v*T 1

(75)

-/3C5fg9;%- 3g9

!@GJIGW~~VJ~A",9 V V T@}W9 LN KML$ VPL" 9&"R" LW~VJƒ W}UKEK‚UV ",9 V V T6}89 L" $%&WIV

$ &=T=VS"K K‚fG=N LN/",9JG% VhQ

7" d7 1

0 *)& $ }=~K L~VfVJ~#JVJI" L&bN-"h&#(2K fV G=~(& I!LK‚8$ Q

778" 1

! K }fTh &#(8K‚UVHmW9 VJI$&b~#L%% G-"lV * LK  &b}WNfT=GJI %,&bNUT@LK L&bN:" ƒSGWNfT

K fV "lV3%,&bNUT & IT=VJI!* GfV V,+@}fGUK L&bNBQ

;`NfG=~#" L" &#( !@GJIGJIV G=~W(\&WI -; A" Q

! IVS"lVJI&JGUKML&bN &#( "sW$9W~V3% KML% "K I } % K‚}WIV L"N !@GJIGJIV G=~Q

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