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Licensed Unlicensed Requires Authentication Published by De Gruyter November 23, 2019

A second-order discretization for forward-backward SDEs using local approximations with Malliavin calculus

  • Riu Naito and Toshihiro Yamada EMAIL logo

Abstract

The paper proposes a new second-order discretization method for forward-backward stochastic differential equations. The method is given by an algorithm with polynomials of Brownian motions where the local approximations using Malliavin calculus play a role. For the implementation, we introduce a new least squares Monte Carlo method for the scheme. A numerical example is illustrated to check the effectiveness.

Award Identifier / Grant number: 19K13736

Funding statement: This work is supported by JSPS KAKENHI (Grant Number 19K13736) from MEXT, Japan.

A Basics of Malliavin calculus and useful lemmas

We briefly summarize Malliavin calculus which is necessary for the main section and the discussion below. See [7, 11] for details of Malliavin calculus. On the probability space (Ω,,P), where

Ω={w:[0,T]d;wis continuous,w(0)=0},

is the Borel field over Ω and P is the Wiener measure, define W:[0,T]×Ωd as W(t,w)=Wt(w)=w(t), wΩ, t[0,T]. Then {Wt}t is a d-dimensional Brownian motion under P. Let 𝒮 be the space of Wiener functionals

𝒮={F=f(W(h1),,W(hn));fCp(n),hiL2([0,T];d),i=1,,n,n1},

where W(h)=0Th(s)dWs=k=1d0Thk(s)dWsk is the Wiener integral for hL2([0,T];d). Let D be the Malliavin derivative operator D:𝒮L2([0,T];d) given by DF=i=1nif(W(h1),,W(hn))hi or

Dk,tF=i=1nif(W(h1),,W(hn))hik(t),t[0,T],k=1,,d.

For j, let DjF=D(Dj-1F) for F𝒮. Since the operator D is closable, the domain of D can be extended from 𝒮 to 𝔻1,p, p1, where 𝔻k,q is the completion of 𝒮 in Lq(Ω) with respect to the norm

Fk,q:-[E[|F|q]+j=1kE[DjFL2([0,T]j)q]]1q.

Moreover, we write 𝔻:-p1j1𝔻j,p. For F=(F1,,Fm)(𝔻)m, γF denotes the Malliavin covariance matrix associated to F given by

[σF]ij:-DFi,DFjL2[0,T],1i,jm.

We say that F=(F1,,Fm)(𝔻)m satisfies the nondegenerate condition if the matrix σF is invertible a.s., and it follows det(σF)-1p1Lp(Ω). Also, we define the divergence operator δ:DomδL2(Ω), where DomδL2(Ω×[0,T];d) is

Domδ:-{uL2(Ω×[0,T],d);|E[DF,uL2[0,T]]|cF2for somec>0,for allF𝔻1,2}.

For F𝔻1,2 and uL2(Ω×[0,T];d), we have E[DF,uL2([0,T])]=E[Fδ(u)]. Note that one has

E[0TDk,tFutkdt]=E[Fδk(uk)],k=1,,d,

and δ(u)=k=1dδk(uk). For G𝔻1,2 and hL2(Ω×[0,T];), we have

δk(Gh)=Gδk(h)-0TDk,tGhtdt,k=1,,d.

The integration by parts on Wiener space is given as follows.

Proposition A.1.

Let F=(F1,,Fm)(D)m be a nondegenerate functional and GD. Let fCb(Rm), and let α=(α1,,αk){1,,d}k be a multi-index of length kN. Then there exists Hα(F,G)D such that E[αf(F)G]=E[f(F)Hα(F,G)]. Here, the weight Hα(F,G) is given recursively by

H(i)(F,G)=j=1Nk=1dδk(G(σF-1)ijDk,Fj),i=1,,m,

and Hα(F,G)=H(αk)(F,H(α1,,αk-1)(F,G)).

We define the space of Watanabe distributions 𝔻- on Ω given as the dual of the space of smooth Wiener functionals 𝔻. The generalized expectation F,G for F𝔻- and G𝔻 is defined as the coupling. Let 𝒮(m) be the space of the Schwartz distributions. Then, for T𝒮(m) and F(𝔻)m, we have T(F)𝔻- and αT(F),G=T(F),Hα(F,G) for any multi-index α and G𝔻. In particular, for the delta function δy𝒮(m) mass at yd, δyF𝔻- is well-defined. For a bounded Borel function f on m and G𝔻,

E[f(F)G]=mf(y)δy(F),Gdy.

For more details on computation with Watanabe distributions, see [12], for example.

Hereafter, let I(i1,,ik)(t,s), (i1,,ik){0,1,,d}k, be the iterated Itô integrals given by

I(i1,,ik)(t,s)=t<t1<<tk<sdWt1i1dWtkik.

Here, the notation Wt0=t is used.

We list the following technical lemmas (Lemmas A.2A.7) which are used in Appendix B.

Lemma A.2.

I(i11,i21)(t,s)I(i12,i22)(t,s)=I(i11,i21,i12,i22)(t,s)+I(i12,i11,i21,i22)(t,s)+I(i11,i12,i21,i22)(t)+I(0,i21,i22)(t,s)𝟏{i12=i110}+I(i11,0,i22)(t,s)𝟏{i12=i210}+I(i12,i22,i11,i21)(t,s)+I(i11,i12,i22,i21)(t,s)+I(i12,i11,i22,i21)(t,s)+I(0,i22,i21)(t,s)𝟏{i11=i120}+I(i12,0,i21)(t,s)𝟏{i11=i220}+I(i11,i12,0)(t,s)𝟏{i21=i220}+I(i12,i11,0)(t,s)𝟏{i21=i220}+I(0,0)(t,s)𝟏{i11=i120}𝟏{i21=i220}.

Proof.

See [10], for example. ∎

Lemma A.3.

I(i11,i21)(t,s)I(i12,i22,i32)(t,s)=I(i11,i21,i12,i22,i32)(t,s)+I(i12,i11,i21,i22,i32)(t,s)+I(i11,i12,i21,i22,i32)(t,s)+I(0,i21,i22,i32)(t,s)𝟏{i12=i110}+I(i11,0,i22,i32)(t,s)𝟏{i12=i210}+I(i12,i22,i11,i21,i32)(t,s)+I(i11,i12,i22,i21,i32)(t,s)+I(i12,i11,i22,i21,i32)(t,s)+I(0,i22,i21,i32)(t,s)𝟏{i11=i120}+I(i12,0,i21,i32)(t,s)𝟏{i11=i220}+I(i11,i12,0,i32)(t,s)𝟏{i21=i220}+I(i12,i11,0,i32)(t,s)𝟏{i21=i220}+I(0,0,i32)(t,s)𝟏{i11=i120}𝟏{i21=i220}+I(i12,i22,i11,i32,i21)(t,s)+I(i11,i12,i22,i32,i21)(t,s)+I(i12,i11,i22,i32,i21)(t,s)+I(0,i22,i32,i21)(t,s)𝟏{i11=i120}+I(i12,0,i32,i21)(t,s)𝟏{i11=i220}+I(i12,i22,i32,i11,i21)(t,s)+I(i12,i22,0,i21)(t,s)𝟏{i32=i110}+{I(i12,i22,i11,0)(t,s)+I(i11,i12,i22,0)(t,s)+I(i12,i11,i22,0)(t,s)+I(0,i22,0)(t,s)𝟏{i11=i120}+I(i12,0,0)(t,s)𝟏{i11=i220}}𝟏{i21=i320}.

Proof.

See [10], for example. ∎

Lemma A.4.

Let

Δ={(s1,,sr)r; 0s1<s2<<srT}.

Let F(D)N, gCb(RN), γ{1,,N}k, kN, and let h be a L2(Δ)-valued Wiener functional such that s1h(s1,,sr) is adapted for fixed s1<s2<<sr. Also, let α{0,1,,d}r such that #{k;αk0}1 (i.e. α=(r<2r)). For e{1,,r} such that αe0, we have

E[γg(F)ti<s1<<sr<ti+1h(s1,,sr)dWs1α1dWsrαr]=j=1NE[jγg(F)ti<s1<<sr<ti+1Dαe,seFjh(s1,,sr)dWs1β1dWsrβr]

for a multi-index β satisfying β=(α1,,αe-1,0,αe+1,,αr) (i.e. |β|=r, β=+1).

Proof.

Apply the duality formula.∎

Lemma A.5.

Let I=(i1,,ik){1,,N}k, kN and (α1,,αr){0,1,,d}r, rN. Then there exist an integer 1, multi-indices βi and nondecreasing functions ci() and hiCb(RN), i=1,,, such that

1hqE[Iψ(X¯ti+1ti,x)I(α1,,αr)(ti,ti+1)]=hr-qi=1E[βif(X¯ti+1ti,x)]ci(h)hi(x)

for all ψCb(RN) and qR.

Proof.

See [10], for example. ∎

Lemma A.6.

δy(Wti,ti+1),I(i1,i2)(ti,ti+1)=δy(Wti,ti+1),12{Wti,ti+1i1Wti,ti+1i2-h𝟏{i1=i20}},
δy(Wti,ti+1),I(i1,i2,i3)(ti,ti+1)=δy(Wti,ti+1),16{Wti,ti+1i1Wti,ti+1i2Wti,ti+1i3-hWti,ti+1i1𝟏{i2=i30}-hWti,ti+1i2𝟏{i1=i30}-hWti,ti+1i3𝟏{i1=i20}},
δy(Wti,ti+1),I(i1,i2,0)(ti,ti+1)=δy(Wti,ti+1),I(i1,0,i2)(t)=δy(Wt),I(0,i1,i2)(ti,ti+1)=δy(Wt){Wti,ti+1i1Wti,ti+1i2-h𝟏{i1=i20}}16h,
δy(Wti,ti+1),I(i1,0,0)(ti,ti+1)=δy(Wti,ti+1),I(0,i1,0)(ti,ti+1)=δy(Wti,ti+1),I(0,0,i1)(ti,ti+1)=δy(Wti,ti+1),Wti,ti+1i116h2,
δy(Wti,ti+1),I(i1,i2,i3,0)(ti,ti+1)=δy(Wti,ti+1),{Wti,ti+1i1Wti,ti+1i2Wti,ti+1i3-hWti,ti+1i1𝟏{i2=i30}-hWti,ti+1i2𝟏{i1=i30}-hWti3𝟏{i1=i20}}124h,
δy(Wti,ti+1),I(i1,i2,0,0)(ti,ti+1)=δy(Wti,ti+1),{Wti,ti+1i1Wti,ti+1i2-h𝟏{i1=i20}}124h2.

Proof.

See [10], for example. ∎

Lemma A.7.

The following formulas hold:

H(l)(X¯ti+1x,ti,{Wti,ti+1i1Wti,ti+1i2-h𝟏{i1=i20}})=1tj=1Ni3=1d(A-1)lj(x)Vi3j(x){Wti,ti+1i1Wti,ti+1i2Wti,ti+1i3-hWti,ti+1i3𝟏{i1=i200}-hWti,ti+1i1𝟏{i2=i30}-hWti,ti+1i2𝟏{i1=i30}},
H(l)(X¯ti+1x,ti,16{Wti,ti+1i1Wti,ti+1i2Wti,ti+1i3-hWti,ti+1i1𝟏{i2=i30}-hWti,ti+1i2𝟏{i1=i30}-hWti,ti+1i3𝟏{i1=i20}})=1hj=1Ni4=1d(A-1)lj(x)Vi4j(x)16{Wti,ti+1i1Wti,ti+1i2Wti,ti+1i3Wti,ti+1i4-hWti,ti+1i1Wti,ti+1i4𝟏{i2=i30}-hWti,ti+1i2Wti,ti+1i4𝟏{i1=i30}-hWti,ti+1i3Wti,ti+1i4𝟏{i1=i20}-hWti,ti+1i2Wti,ti+1i3𝟏{i1=i40}-hWti,ti+1i1Wti,ti+1i3𝟏{i2=i40}-hWti,ti+1i1Wti,ti+1i2𝟏{i3=i40}+h2𝟏{i1=i40}𝟏{i2=i30}+h2𝟏{i2=i40}𝟏{i1=i30}+h2𝟏{i3=i40}𝟏{i1=i20}},
H(l,m)(X¯ti+1x,ti,Wti,ti+1i1Wti,ti+1i2-h𝟏{i1=i20})=1h2j1,j2=1Nk1,k2=1d(A-1)lj2(x)Vk2j2(x)(A-1)mj1(x)Vk1j1(x){Wti,ti+1i1Wti,ti+1i2Wti,ti+1k1Wti,ti+1k2-hWti,ti+1k1Wti,ti+1k2𝟏{i1=i20}-hWti,ti+1i1Wti,ti+1k2𝟏{i2=k10}-hWti,ti+1i2Wti,ti+1k2𝟏{i1=k10}-hWti,ti+1i2Wti,ti+1k1𝟏{i1=k20}-hWti,ti+1i1Wti,ti+1k1𝟏{i2=k20}-hWti,ti+1i1Wti,ti+1i2𝟏{k1=k20}+h2𝟏{k1=k20}𝟏{i1=i20}+h2𝟏{i1=k20}𝟏{b=k10}+h2𝟏{i2=k20}𝟏{i1=k10}},
H(l,m)(X¯ti+1x,ti,Wti,ti+1i1)=1h2j1,j2Nk1,k2=1d(A-1)lj2(x)Vk2j2(x)(A-1)mj1(x)Vk1j1(x)×{Wti,ti+1i1Wti,ti+1k1Wti,ti+1k2-hWti,ti+1k2𝟏{i1=k10}-hWti,ti+1a𝟏{k1=k20}-hWti,ti+1k1𝟏{i1=k20}},
H(l,m)(X¯ti+1x,ti,1)=1h2j1,j2Nk1,k2=1d(A-1)lj2(x)Vk2j2(x)(A-1)mj1(x)Vk1j1(x)(Wti,ti+1k1Wti,ti+1k2-h𝟏{k1=k20}),
H(l,m,p)(X¯ti+1x,ti,1)=1h3j1,j2,j3,k1,k2,k3=1d(A-1)lj3(x)Vk3(x)(A-1)mj2(x)Vk2(x)(A-1)pj1(x)Vk1(x)×[Wti,ti+1k1Wti,ti+1k2Wti,ti+1k3-hWti,ti+1k3𝟏{k1=k20}-hWti,ti+1k1𝟏{k2=k30}-hWti,ti+1k2𝟏{k1=k30}].

Proof.

See [10], for example. ∎

B Local approximations

The following local approximations (Theorems B.1 and B.2) with ϑti+1ti,x and ϱti+1ti,x introduced in Section 2.2 are needed to prove the main result.

Theorem B.1.

For ψCb(RN;R), there exists C>0 such that

|E[ψ(Xti+1ti,x)]-E[ψ(X¯ti+1ti,x)ϑti+1ti,x]|Ch3

for all nN, xRN and i=0,1,,n-1.

Proof.

See [10, Proposition 3.9]. ∎

The expectation with Crisan–Manolarakis’s 𝒵ti+1ti,x is approximated as follows.

Theorem B.2.

For ψCb(RN;R), there exists C>0 such that

|E[ψ(Xti+1ti,x)𝒵ti+1ti,x]-E[ψ(X¯ti+1ti,x)ϱti+1ti,x]|Ch3

for all nN, xRN and i=0,1,,n-1.

Proof.

By the expansion of g(Xti+1ti,x) around g(X¯ti+1ti,x) with the stochastic Taylor expansion (see [8])

Xti+1ti,x=X¯ti+1ti,x+j1,j2=0dLjVk(x)I(j,k)(ti,ti+1)+j1,j2,j3=0dLj1Lj2Vj3(x)I(j1,j2,j3)(ti,ti+1)+rti+1ti,x

with the residual rti+1ti,x, we get

(B.1)E[g(Xti+1ti,x)𝒵ti+1ti,l]=E[(g(X¯ti+1ti,x)+p=1Npg(X¯ti+1ti,x)j,k=0d{LjVkp(x)I(j,k)(ti,ti+1)+l=0dLjLkVlp(x)I(j,k,l)(ti,ti+1)}+12p,q=1Npqg(X¯ti+1ti,x)j1,j2,k1,k2=0d{Lj1Vj2p(x)Lk1Vk2q(x)I(j1,j2)(ti,ti+1)I(k1,k2)(ti,ti+1)+2j3=0dLj1Lj2Vj3p(x)Lk1Vk2q(x)I(j1,j2,j3)(ti,ti+1)I(k1,k2)(ti,ti+1)}+R+R)𝒵ti+1ti,l],

where 𝒵ti+1ti,l=4Wti,ti+1lh-6I(0,l)(ti,ti+1)h2,

R=16p1,p2,p3=1Np1p2p3g(X^ti+1ti,x)i1,i2,j1,j2,k1,k2=0dtiti+1tisLi1Vi2p1(Xrti,x)dWri1dWsi2×titi+1tisLj1Vj2p2(Xrti,x)dWrj1dWsj2titi+1tisLk1Vk2p3(Xrti,x)dWrk1dWsk2

with X^ti+1ti,x:-θXti+1ti,x+(1-θ)X¯ti+1ti,x, θ(0,1), and

R=p=1Npg(X¯ti+1ti,x)i1,i2,i3,i4=0dti<u<r<s<t<ti+1Li1Li2Li3Vi4p(Xuti,x)dWui1dWri2dWsi3dWti4+p,q=1Npqg(X¯ti+1ti,x)i1,i2,i3,i4=0dLi1Vi2p(Xuti,x)Ii1,i2(ti,ti+1)×ti<u<r<s<t<ti+1Lj1Lj2Lj3Vj4p(Xuti,x)dWuj1dWrj2dWsj3dWtj4+12p,q=1Npqg(X¯ti+1ti,x)i1,i2,i3,i4,j1,j2,j3,j4=0dti<r<s<t<ti+1Li1Li2Vi3p(Xrti,x)dWri1dWsi2dWti3×ti<r<s<t<ti+1Lj1Lj2Vj3p(Xrti,x)dWrj1dWsj2dWtj3.

Some terms in (B.1) will be O(h3). To check this, we estimate the upper bounds of the terms E[R𝒵ti+1ti,l] and E[R𝒵ti+1ti,l]. Using the Itô formula, we obtain

|E[R𝒵ti+1ti,l]|=|γ{1,,N}3E[γg(X^ti+1ti,x){1hα={0,1,,d}r,|α|=r4, 7α13ti<s1<<sr<ti+1ψγ,α1(s1,,sr)dWs1α1dWsrαr+1h2α={0,1,,d}r,|α|=r5, 9α15ti<s1<<sr<ti+1ψγ,α2(s1,,sr)dWs1α1dWsrαr}]|

for some ψγ,αj, j=1,2, are L2(Δ)-valued Wiener functionals such that s1hγ,αj(s1,,sr) is adapted for fixed s1<s2<<sr. Note that, for α{0,1,,d}r such that 8α13, we immediately have

|E[γg(X^ti+1ti,x)1hti<s1<<sr<ti+1ψγ,α1(s1,,sr)dWs1α1dWsrαr]|C|γ|gh8/2-1=C3gh3

by the Cauchy–Schwarz inequality with

ti<s1<<sr<ti+1ψγ,α1(s1,,sr)dWs1α1dWsrαr2=O(hα/2).

Also, for α{0,1,,d}r, r5, such that 10α15, we get

|E[γg(X^ti+1ti,x)1h2ti<s1<<sr<ti+1ψγ,α2(s1,,sr)dWs1α1dWsrαr]|C|γ|gh10/2-2=C3gh3.

For α{0,1,,d}r, r4, such that α=7, there exists e{1,,r} such that αe0, and we can apply the duality formula to get

(B.2)E[γg(X^ti+1ti,x)1hti<s1<<sr<ti+1ψγ,α1(s1,,sr)dWs1α1dWsrαr]==1NE[γg(X^ti+1ti,x)ti<s1<<sr<ti+1Dαe,seX^ti+1ti,x,1hψγ,α1(s1,,sr)dWs1β1dWsrβr]

for a multi-index β satisfying β=(α1,,αe-1,0,αe+1,,αr) (i.e. |β|=r, β=8). Using the Cauchy–Schwarz inequality and the fact that X^𝔻,

|E[γg(X^ti+1ti,x)1hti<s1<<sr<ti+1ψγ,α1(s1,,sr)dWs1α1dWsrαr]|C|γ|+1gh8/2-1=C4gh3.

Also, using a similar computation in (B.2), we can show that, for α{0,1,,d}r such that α=9,

|E[γg(X^ti+1ti,x)1h2ti<s1<<sr<ti+1ψγ,α2(s1,,sr)dWs1α1dWsrαr]|C|γ|+1gh10/2-2=C4gh3.

Therefore, we have |E[R𝒵ti+1ti,x]|Ch3. The same argument can be applied to the following:

|E[R𝒵ti+1ti,l]|=|γ{1,,N}1E[γg(X^ti+1ti,x)×{1hα={0,1,,d}r,|α|=r4, 5α9ti<s1<<sr<ti+1ϕγ,α1(s1,,sr)dWs1α1dWsrαr+1h2α={0,1,,d}r,|α|=r5, 7α11ti<s1<<sr<ti+1ϕγ,α2(s1,,sr)dWs1α1dWsrαr}]+γ{1,,N}2E[γg(X^ti+1ti,x)×{1hα={0,1,,d}r,|α|=r4, 7α13ti<s1<<sr<ti+1χγ,α1(s1,,sr)dWs1α1dWsrαr+1h2α={0,1,,d}r,|α|=r5, 9α15ti<s1<<sr<ti+1χγ,α2(s1,,sr)dWs1α1dWsrαr}]|

for some ϕγ,αi,χγ,αi, i=1,2. Then we attain |E[R𝒵ti+1ti,x]|Ch3. Since E[R𝒵ti+1ti,l]=O(h3) and E[R𝒵ti+1ti,l]=O(h3), these can be treated as the residual of the expansion of E[g(Xti+1ti,x)𝒵ti+1ti,l]. We have

E[g(Xti+1ti,x)𝒵ti+1ti,l]=E[(g(X¯ti+1ti,x)+p=1Npg(X¯ti+1ti,x)j,k=0d{LjVkp(x)I(j,k)(ti,ti+1)+m=0dLjLkVmp(x)I(j,k,m)(ti,ti+1)}+12p,q=1Npqg(X¯ti+1ti,x)j1,j2,k1,k2=0d{Lj1Vj2p(x)Lk1Vk2q(x)I(j1,j2)(ti,ti+1)I(k1,k2)(ti,ti+1)+2j3=0dLj1Lj2Vj3p(x)Lk1Vk2q(x)I(j1,j2,j3)(ti,ti+1)I(k1,k2)(ti,ti+1)})𝒵ti+1ti,l]+O(h3).

We further analyze the approximation terms. Using Lemma A.2 and Lemma A.3, we have

E[g(Xti+1ti,x)𝒵ti+1ti,l]
  =E[g(X¯ti+1ti,x)𝒵ti+1ti,l+p=1Npg(X¯ti+1ti,x)(j,k=0dLjVkp(x)
         ×{4h(I(j,k,l)(ti,ti+1)+I(l,j,k)(ti,ti+1)+I(j,l,k)(ti,ti+1)
               +I(j,0)(ti,ti+1)𝟏{k=l0}+I(0,k)(ti,ti+1)𝟏{j=l0})
            -6h2(I(j,k,0,l)(ti,ti+1)+I(0,j,k,l)(ti,ti+1)+I(i,0,j,l)(ti,ti+1)
               +I(0,l,j,k)(ti,ti+1)+I(i,0,l,j)(ti,ti+1)+I(0,i,l,j)(ti,ti+1)
               +I(0,0,k)(ti,ti+1)𝟏{j=l0}+I(j,0,0)(ti,ti+1)𝟏{k=l0}+I(0,j,0)(ti,ti+1)𝟏{k=l0})}
      +e,j,k,l=0dLeLjVkp(x)
         ×{4h(I(0,j,k)(ti,ti+1)𝟏{e=l0}+I(e,0,k)(ti,ti+1)𝟏{j=l0}+I(e,j,0)(ti,ti+1)𝟏{k=l0})
            -6h2(I(0,0,j,k)(ti,ti+1)𝟏{e=l0}+I(e,0,0,k)(ti,ti+1)𝟏{j=l0}
               +I(0,e,0,k)(ti,ti+1)𝟏{j=l0}+I(e,j,0,0)(ti,ti+1)𝟏{l=k0}
               +I(0,e,j,0)(ti,ti+1)𝟏{l=k0}+I(e,0,j,0)(ti,ti+1)𝟏{l=k0})})
   +12p,q=1Npqg(X¯ti+1ti,x)(j1,j2,k1,k2=0dLj1Vj2p(x)Lk1Vk2q(x)
         ×{4h(I(0,0,j2)(ti,ti+1)(𝟏{k1=j10,k2=l0}+𝟏{k1=l0,j1=k20})
               +I(0,0,k2)(ti,ti+1)(𝟏{j1=k10,l=j20}+𝟏{j1=l0,k1=j20})
               +I(0,0,l)(ti,ti+1)𝟏{j1=k10,j2=k20}+I(0,l,0)(ti,ti+1)𝟏{j1=k10,j2=k20}
               +I(0,k1,0)(ti,ti+1)𝟏{j1=l0,j2=k20}+I(0,j1,0)(ti,ti+1)𝟏{k1=l0,j2=k20}
               +I(j1,0,0)(ti,ti+1)𝟏{k1=l0,j2=k2}+I(k1,0,0)(ti,ti+1)𝟏{j1=l0,j2=k20}
               +I(l,0,0)(ti,ti+1)𝟏{j1=k10,j2=k20}+I(0,j2,0)(ti,ti+1)𝟏{j1=k10,k2=l0}
               +I(j1,0,0)(ti,ti+1)𝟏{j2=k10,k2=l0}+I(0,k2,0)(ti,ti+1)𝟏{j1=k10,j2=l0}
               +I(k1,0,0)(ti,ti+1)𝟏{j1=k20,j2=l0})
            -6h2(3I(0,0,0,l)(ti,ti+1)𝟏{j1=k10,j2=k20}
               +I(0,0,0,j2)(2𝟏{j1=k10,k2=l0}+𝟏{k1=l0,j1=k20})
               +2I(0,0,j2,0)(ti,ti+1)𝟏{j1=k10,k2=l0}+I(0,j2,0,0)(ti,ti+1)𝟏{j1=k10,k2=l0}
               +2I(j1,0,0,0)(ti,ti+1)𝟏{j2=k10,k2=l0}+I(0,j1,0,0)(ti,ti+1)𝟏{j2=k10,k2=l0}
               +2I(0,0,k2,0)(ti,ti+1)𝟏{j1=k10,j2=l0}+I(0,k2,0,0)(ti,ti+1)𝟏{j1=k10,j2=l0}
               +2I(k1,0,0,0)(ti,ti+1)𝟏{j1=k20,j2=l0}+I(0,k1,0,0)(ti,ti+1)𝟏{j1=k20,j2=l0}
               +2I(0,0,l,0)(ti,ti+1)𝟏{j1=k10,j2=k20}+I(0,0,j1,0)(ti,ti+1)𝟏{k1=l0,j2=k20}
               +I(0,0,k1,0)(ti,ti+1)𝟏{j1=l0,j2=k20}+I(0,l,0,0)(ti,ti+1)𝟏{j1=k10,j2=k20}
               +I(0,k1,0,0)(ti,ti+1)𝟏{j1=l0,j2=k20}+I(k1,0,0,0)(ti,ti+1)𝟏{j1=l0,j2=k20}
               +I(0,j1,0,0)(ti,ti+1)𝟏{k1=l0,j2=k20}+I(j1,0,0,0)(ti,ti+1)𝟏{k1=l0,j2=k20})}
      +2j3=0dLj1Lj2Vj3p(x)Lk1Vk2q(x)
         ×{4h(I0,0,0(ti,ti+1)𝟏{j1=k10,j2=k20,j3=l0})
            -6h2I0,0,0,0(ti,ti+1)(2𝟏{j1=k10,j2=k20,j3=l0}
               +2𝟏{j1=k10,j2=l0,j3=k20}+2𝟏{j1=l0,j2=k10,j3=k20})})]+O(h3).

Here, the terms corresponding to the case r-q3 in Lemma A.5 are treated as the residual O(h3) in the above. Using Lemma A.6, we can convert the iterated stochastic integrals to a linear sum of Brownian polynomials

E[g(Xti+1ti,x)𝒵ti+1ti,l]
  =E[g(X¯ti+1ti,x)Wti,ti+1lh+p=1Npg(X¯ti+1ti,x)(j,k=0dLjVkp(x)
         ×{2h(𝕎(j,k,l)(ti,ti+1)+𝕎(j,0)(ti,ti+1)𝟏{k=l0}+𝕎(0,k)(ti,ti+1)𝟏{j=l0})
            -12h2(3𝕎(j,k,0,l)(ti,ti+1)+2𝕎(0,0,k)(ti,ti+1)𝟏{j=l0}+4𝕎(j,0,0)(ti,ti+1)𝟏{k=l0})}
      +e,j,k,l=0dLeLjVkp(x)
         ×{23h(𝕎(0,j,k)(ti,ti+1)𝟏{h=l0}+𝕎(e,0,k)(ti,ti+1)𝟏{j=l0}+𝕎(e,j,0)(ti,ti+1)𝟏{k=l0})
            -14h2(𝕎(0,0,j,k)(ti,ti+1)𝟏{e=l0}
               +2𝕎(e,0,0,k)(ti,ti+1)𝟏{j=l0}+3𝕎(e,j,0,0)(ti,ti+1)𝟏{l=k0})})
   +12p,q=1Npqg(X¯ti+1ti,x)(j1,j2,k1,k2=0dLj1Vj2p(x)Lk1Vk2q(x)
         ×{23h(𝕎(0,0,j2)(ti,ti+1)(2𝟏{k1=j10,k2=l0}+𝟏{k1=l0,j1=k20})
               +𝕎(0,0,k2)(ti,ti+1)(2𝟏{j1=k10,l=j20}+𝟏{j1=l0,k1=j20})
               +𝕎(0,0,l)(ti,ti+1)(3𝟏{j1=k10,j2=k20})
               +𝕎(0,k1,0)(ti,ti+1)(2𝟏{j1=l0,j2=k20}+𝟏{j1=k20,j2=l0})
               +𝕎(0,j1,0)(2𝟏{k1=l0,j2=k20}+𝟏{j2=k10,k2=l0}))
            -6h2(𝕎(0,0,0,j2)(ti,ti+1)(5𝟏{j1=k10,k2=l0}+𝟏{k1=l0,j1=k20})
               +𝕎(j1,0,0,0)(ti,ti+1)(3𝟏{j2=k10,k2=l0}+3𝟏{k1=l0,j2=k2})
               +𝕎(0,0,k2,0)(ti,ti+1)(5𝟏{j1=k10,j2=l0}+𝟏{j1=l0,j2=k10})
               +𝕎(k1,0,0,0)(ti,ti+1)(3𝟏{j1=k20,j2=l0}+3𝟏{j1=l0,j2=k20})
               +𝕎(0,0,l,0)(ti,ti+1)6𝟏{j1=k10,j2=k20})}
      +2j1,j2,j3,k1,k2=0dLj1Lj2Vj3p(x)Lk1Vk2q(x)
         ×{23h2(𝕎0,0,0(ti,ti+1)𝟏{j1=k10,j2=k20,j3=l0})
            -14h2(2𝟏{j1=k10,j2=k20,j3=l0}
               +2𝟏{j1=k10,j2=l0,j3=k20}+2𝟏{j1=l0,j2=k10,j3=k20})})]+O(h3).

Applying the integration by parts formulas in Lemma A.7, we get

E[g(Xti+1ti,x)𝒵ti+1ti,l]
  =E[g(X¯ti+1ti,x)Wti,ti+1lh+1hp,q=1Ng(X¯ti+1ti,x)(j,k=0,α=1dLjVkp(x)(A-1)pq(x)Vαq(x)
         ×{2h(𝕎(j,k,l,α)(ti,ti+1)+𝕎(j,0,α)(ti,ti+1)𝟏{k=l0}+𝕎(0,k,α)(ti,ti+1)𝟏{j=l0})
            -12h2(3𝕎(j,k,0,l,α)(ti,ti+1)
               +2𝕎(0,0,k,α)(ti,ti+1)𝟏{j=l0}+4𝕎(j,0,0,α)(ti,ti+1)𝟏{k=l0})}
      +e,j,k=0,α=1dLeLjVkp(x)(A-1)(x)pqVαq(x)
         ×{23h(𝕎(0,j,k,α)(ti,ti+1)𝟏{e=l0}
               +𝕎(e,0,k,α)(ti,ti+1)𝟏{j=l0}+𝕎(e,j,0,α)(ti,ti+1)𝟏{k=l0})
            -14h2(𝕎(0,0,j,k,α)(ti,ti+1)𝟏{e=l0}
               +2𝕎(e,0,0,k,α)(ti,ti+1)𝟏{j=l0}+3𝕎(e,j,0,0,α)(ti,ti+1)𝟏{l=k0})})
   +12h2p,q,r,s=1Ng(X¯ti+1ti,x)(j1,j2,k1,k2=0,α,β=1dLj1Vj2p(x)Lk1Vk2q(x)(A-1)pr(x)(A-1)qs(x)Vαr(x)Vβs(x)
         ×{23h(𝕎(0,0,j2,α,β)(ti,ti+1)(2𝟏{k1=j10,k2=l0}+𝟏{k1=l0,j1=k20})
               +𝕎(0,0,k2,α,β)(ti,ti+1)(2𝟏{j1=k10,l=j20}+𝟏{j1=l0,k1=j20})
               +𝕎(0,0,l,α,β)(ti,ti+1)(3𝟏{j1=k10,j2=k20})
               +𝕎(0,k1,0,α,β)(ti,ti+1)(2𝟏{j1=l0,j2=k20}+𝟏{j1=k20,j2=l0})
               +𝕎(0,j1,0,α,β)(2𝟏{k1=l0,j2=k20}+𝟏{j2=k10,k2=l0}))
            -6h2(𝕎(0,0,0,j2,α,β)(ti,ti+1)(5𝟏{j1=k10,k2=l0}+𝟏{k1=l0,j1=k20})
               +𝕎(j1,0,0,0,α,β)(ti,ti+1)(3𝟏{j2=k10,k2=l0}+3𝟏{k1=l0,j2=k2})
               +𝕎(0,0,k2,0,α,β)(ti,ti+1)(5𝟏{j1=k10,j2=l0}+𝟏{j1=l0,j2=k10})
               +𝕎(k1,0,0,0,α,β)(ti,ti+1)(3𝟏{j1=k20,j2=l0}+3𝟏{j1=l0,j2=k20})
               +𝕎(0,0,l,0,α,β)(ti,ti+1)6𝟏{j1=k10,j2=k20})}
      +2j1,j2,j3,k1,k2=0,α,β=1dLj1Lj2Vj3p(x)Lk1Vk2q(x)(A-1)pr(x)(A-1)qs(x)Vαr(x)Vβs(x)
         ×{23(𝕎(α,β)(ti,ti+1)𝟏{j1=k10,j2=k20,j3=l0})
            -12𝕎(α,β)(ti,ti+1)(𝟏{j1=k10,j2=k20,j3=l0}
                  +𝟏{j1=k10,j2=l0,j3=k20}+𝟏{j1=l0,j2=k10,j3=k20})})]+O(h3).

C Proof of the main theorem (Theorem 2.4)

We define the following:

R¯n-1Zg(x)=E[g(X¯tntn-1,x)ϱtntn-1,x]+hE[f(tn,X¯tntn-1,x,g(X¯tntn-1,x),g(X¯tntn-1,x)V(X¯tntn-1,x))ϱtntn-1,x],
R¯n-1Yg(x)=E[g(X¯tntn-1,x)ϑtntn-1,x]+h2f(tn,x,R¯n-1Yg(x),R¯n-1Zg(x))+E[h2f(tn,X¯tntn-1,x,g(X¯tntn-1,x),g(X¯tntn-1,x)V(X¯tntn-1,x))ϑtntn-1,x],
(C.1)R¯iZR¯i+1ZR¯n-1Zg(x)=E[R¯i+1YR¯n-1Y(X¯ti+1ti,x)ϱti+1ti,x]+hE[f(ti+1,X¯ti+1ti,x,R¯i+1YR¯n-1Yg(X¯ti+1ti,x),R¯i+1ZR¯n-1Zg(X¯ti+1ti,x))ϱti+1ti,x],
R¯iYR¯i+1YR¯n-1Yg(x)=E[R¯i+1YR¯n-1Yg(X¯ti+1ti,x)ϑti+1ti,x]+h2f(ti,x,R¯iYR¯n-1Yg(x),R¯iZR¯n-1Zg(x))+E[h2f(ti+1,X¯ti+1ti,x,R¯i+1YR¯n-1Yg(X¯ti+1ti,x),R¯i+1ZR¯n-1Zg(X¯ti+1ti,x))ϑti+1ti,x]

for i=0,1,,n-2 and xN. Then we can see that Y0Mall=R¯0YR¯1YR¯n-1Yg(x0). To obtain the result, we decompose the bound as

(C.2)|Y0-Y0Mall||Y0-R0YR1YRn-1Yg(x0)|+|R0YR1YRn-1Yg(x0)-R¯0YR¯1YR¯n-1Yg(x0)|,

where R0YR1YRn-1Yg(x) is defined by

Rn-1Zg(x)=E[g(Xtntn-1,x)𝒵tntn-1,x]+hE[f(tn,Xtntn-1,x,g(Xtntn-1,x),g(Xtntn-1,x)V(Xtntn-1,x))𝒵tntn-1,x],
Rn-1Yg(x)=E[g(Xtntn-1,x)]+h2f(tn,x,Rn-1Yg(x),Rn-1Zg(x))+E[h2f(tn,Xtntn-1,x,g(Xtntn-1,x),g(Xtntn-1,x)V(Xtntn-1,x))],
RiZRi+1ZRn-1Zg(x)=E[Ri+1YRn-1Yg(Xti+1ti,x)𝒵ti+1ti,x]+hE[f(ti+1,Xti+1ti,x,Ri+1YRn-1Yg(Xti+1ti,x),Ri+1ZRn-1Zg(Xti+1ti,x))𝒵ti+1ti,x],
RiYRi+1YRn-1Yg(x)=E[Ri+1YRn-1Yg(Xti+1ti,x)]+h2f(ti,x,RiYRn-1Yg(x),RiZRn-1Zg(x))+E[h2f(ti+1,Xti+1ti,x,Ri+1YRn-1Yg(Xti+1ti,x),Ri+1ZRn-1Zg(Xti+1ti,x))]

for i=0,1,,n-2 and xN. We note that it holds Y0CM=R0YR1YRn-1Yg(x0) and

|Y0-R0YR1YRn-1Yg(x0)|=|Y0-Y0CM|=O(1n2),

by [4]. Then, in order to estimate (C.2), it suffices to show the bound of

|R0YR1YRn-1Yg(x)-R¯0YR¯1YR¯n-1Yg(x)|,xN.

The following lemma finishes the proof of Theorem 2.4.

Lemma C.1.

There exists C>0 such that

|R0YR1YRn-1Yg(x)-R¯0YR¯1YR¯n-1Yg(x)|C1n2

for all n1 and xRN.

Proof.

We have

R0YR1YRn-1Yg(x)-R¯0YR¯1YR¯n-1Yg(x)=R0YR1YRn-1Yg(x)-R¯0YR1YRn-1Yg(x)+i=0n-3R¯0YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯iYR¯i+1YRi+2YRn-1Yg(x)+R¯0YR¯1YR¯n-2YRn-1Yg(x)-R¯0YR¯1YR¯n-2YR¯n-1Yg(x),

Here,

R¯iYRi+1YRn-1Yg(x)=E[Ri+1YRn-1Yg(X¯ti+1ti,x)ϑti+1ti,x]+h2f(ti,x,R¯iYRi+1YRn-1Yg(x),R¯iZRi+1ZRn-1Zg(x))+E[h2f(ti+1,X¯ti+1ti,x,Ri+1YRn-1Yg(X¯ti+1ti,x),Ri+1ZRn-1Zg(X¯ti+1ti,x))ϑti+1ti,x]

with

(C.3)R¯iZRi+1ZRn-1Zg(x)=E[Ri+1YRn-1Yg(X¯ti+1ti,x)ϱti+1ti,x]+hE[f(ti+1,X¯ti+1ti,x,Ri+1YRn-1Yg(X¯ti+1ti,x),Ri+1ZRn-1Zg(X¯ti+1ti,x))ϱti+1ti,x],

and

R¯iYR¯i+1YR¯i+k-1YRi+kYRn-1Yg(x)=E[R¯i+1YR¯i+k-1YRi+kYRn-1Yg(X¯ti+1ti,x)ϑti+1ti,x]+h2f(ti,x,R¯iYR¯i+1YR¯i+k-1YRi+kYRn-1Yg(x),R¯iZR¯i+1ZR¯i+k-1ZRi+kZRn-1Zg(x))+h2E[f(ti+1,X¯ti+1ti,x,R¯i+1YR¯i+k-1YRi+kYRn-1Yg(X¯ti+1ti,x),R¯i+1ZR¯i+k-1ZRi+kZRn-1Zg(X¯ti+1ti,x))ϑti+1ti,x]

with

(C.4)R¯iZR¯i+1ZR¯i+k-1ZRi+kZRn-1Zg(x)=E[R¯i+1YR¯i+k-1YRi+kYRn-1Yg(X¯ti+1ti,x)ϱti+1ti,x]+hE[f(ti+1,X¯ti+1ti,x,R¯i+1YR¯i+k-1YRi+kYRn-1Yg(X¯ti+1ti,x),R¯i+1ZR¯i+k-1ZRi+kZRn-1Zg(X¯ti+1ti,x))ϱti+1ti,x]

are recursively defined. For i=0,1,,n-3, we show the bound of

|R¯0YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯iYR¯i+1YRi+2YRn-1Yg(x)|.

Note that we have

R¯0YR¯1YR¯iYRi+1YRi+2YRn-1Yg(x)=E[R¯1YR¯iYRi+1YRi+2YRn-1Yg(X¯t1t0,x)ϑt1t0,x]+T2nf(t0,x,R¯0YR¯1YR¯iYRi+1YRi+2YRn-1Yg(x),R¯0ZR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg(x))+T2nE[f(t1,X¯t1t0,x,R¯1YR¯iYRi+1YRi+2YRn-1Yg(X¯t1t0,x),R¯1ZR¯iZRi+1ZRi+2ZRn-1Zg(X¯t1t0,x))ϑt1t0,x],
R¯0YR¯1YR¯iYR¯i+1YRi+2YRn-1Yg(x)=E[R¯1YR¯iYR¯i+1YRi+2YRn-1Yg(X¯t1t0,x)ϑt1t0,x]+T2nf(t0,x,R¯0YR¯1YR¯iYR¯i+1YRi+2YRn-1Yg(x),R¯0ZR¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg(x))+T2nE[f(t1,X¯t1t0,x,R¯1YR¯iYR¯i+1YRi+2YRn-1Yg(X¯t1t0,x),R¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg(X¯t1t0,x))ϑt1t0,x].

In the following, we use a generic constant C>0 independent of n and x, whose value will be changed from line to line. By using the Lipschitz continuity of f and the estimate |E[ψ(X¯t1t0,x)ϑt1t0,x]|ψC for a bounded function ψ, we have

(C.5)(1-Cn)|R¯0YR¯1YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯1YR¯iYR¯i+1YRi+2YRn-1Yg(x)|CR¯1YR¯iYRi+1YRi+2YRn-1Yg-R¯1YR¯iYR¯i+1YRi+2YRn-1Yg+CR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg-R¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg+(Cn)R¯0ZR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg-R¯0ZR¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg.

For the last term in the right-hand side of the above, we have

|R¯0ZR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg(x)-R¯0ZR¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg(x)|CnR¯1YR¯iYRi+1YRi+2YRn-1Yg-R¯1YR¯iYR¯i+1YRi+2YRn-1Yg+CnR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg-R¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg

by (C.4) and the estimate |E[ψ(X¯t1t0,x)ϱt1t0,x]|ψCn for a bounded function ψ. Then (C.5) can be summarized as

(1-Cn)|R¯0YR¯1YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯1YR¯iYR¯i+1YRi+2YRn-1Yg(x)|CR¯1YR¯iYRi+1YRi+2YRn-1Yg-R¯1YR¯iYR¯i+1YRi+2YRn-1Yg+CR¯1ZR¯iZRi+1ZRi+2ZRn-1Zg-R¯1ZR¯iZR¯i+1ZRi+2ZRn-1Zg.

Inductively, we have

(1-Cn)|R¯1YR¯2YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯1YR¯2YR¯iYR¯i+1YRi+2YRn-1Yg(x)|CR¯2YR¯iYRi+1YRi+2YRn-1Yg-R¯2YR¯iYR¯i+1YRi+2YRn-1Yg+CR¯2ZR¯iZRi+1ZRi+2ZRn-1Zg-R¯2ZR¯iZR¯i+1ZRi+2ZRn-1Zg,
(1-Cn)|R¯iYRi+1YRi+2YRn-1Yg(x)-R¯iYR¯i+1YRi+2YRn-1Yg(x)|CRi+1YRi+2YRn-1Yg-R¯i+1YRi+2YRn-1Yg+CRi+1ZRi+2ZRn-1Zg-R¯i+1ZRi+2ZRn-1Zg.

Then the estimate

|R¯0YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯iYR¯i+1YRi+2YRn-1Yg(x)|

is reduced to that of

Ri+1YRi+2YRn-1Yg-R¯i+1YRi+2YRn-1Yg

and

Ri+1ZRi+2ZRn-1Zg-R¯i+1ZRi+2ZRn-1Zg.

We note that Ri+1YRi+2YRn-1Yg(x) and R¯i+1YRi+2YRn-1Yg(x) are given by

Ri+1YRi+2YRn-1Yg(x)=E[Ri+2YRn-1Yg(Xti+2ti+1,x)]+T2nf(ti+1,x,Ri+1YRi+2YRn-1Yg(x),Ri+1ZRi+2ZRn-1Zg(x))+E[T2nf(ti+2,Xti+2ti+1,x,Ri+2YRn-1Yg(Xti+2ti+1,x),Ri+2ZRn-1Zg(Xti+2ti+1,x))],
R¯i+1YRi+2YRn-1Yg(x)=E[Ri+2YRn-1Yg(X¯ti+2ti+1,x)ϑti+2ti+1,x]+T2nf(ti+1,x,R¯i+1YRi+2YRn-1Yg(x),R¯i+1ZRi+2ZRn-1Zg(x))+E[T2nf(ti+2,X¯ti+2ti+1,x,Ri+2YRn-1Yg(X¯ti+2ti+1,x),Ri+2ZRn-1Zg(X¯ti+2ti+1,x))ϑti+2ti+1,x].

Applying Theorem B.1, we get

(1-Cn)|Ri+1YRi+2YRn-1Yg(x)-R¯i+1YRi+2YRn-1Yg(x)|Ri+2YRn-1YgC1n3+C1n|Ri+1ZRi+2ZRn-1Zg(x)-R¯i+1ZRi+2ZRn-1Zg(x)|+C1n3.

By (C.1) and (C.3) with Theorem B.2, it holds that

|Ri+1ZRi+2ZRn-1Zg(x)-R¯i+1ZRi+2ZRn-1Zg(x)|Ri+2YRn-1YgC1n3+C1n3.

Then, by the estimate

|Ri+2YRn-1Yg(x)|Ri+3YRn-1Yg+Cg+C

and by the fact 11+O(1/n)=1+O(1n), one has

|Ri+1YRi+2YRn-1Yg(x)-R¯i+1YRi+2YRn-1Yg(x)|C1n3,
|Ri+1ZRi+2ZRn-1Zg(x)-R¯i+1ZRi+2ZRn-1Zg(x)|C1n3.

Therefore, for i=0,1,,n-3, we have

|R¯0YR¯iYRi+1YRi+2YRn-1Yg(x)-R¯0YR¯iYR¯i+1YRi+2YRn-1Yg(x)|C1n3.

With a similar argument, we also have

|R0YR1YRn-1Yg(x)-R¯0YR1YRn-1Yg(x)|C1n3,
|R¯0YR¯1YR¯n-2YRn-1Yg(x)-R¯0YR¯1YR¯n-2YR¯n-1Yg(x)|C1n3.

Finally, we get

|R0YR1YRn-1Yg(x)-R¯0YR¯1YR¯n-1Yg(x)|i=1nC1n3=Cn2.

D Some useful results

When N=d, we have simpler representations of ϑti+1ti,x and ϱti+1ti,x,l in Theorems B.1 and B.2 through the Bismut identity (see [1])

(D.1)E[φ(X¯ti+1ti,x)G]=1hE[0tφ(X¯ti+1ti,x)V(x)V-1(x)Gds]=1hE[titi+1Dsφ(X¯ti+1ti,x)V-1(x)Gds]=1hE[φ(X¯ti+1ti,x)k=1dδk([V-1(x)G]k𝟏{titi+1})]=k,l=1dE[φ(X¯ti+1ti,x)1t(V-1)kl(x){GlWti,ti+1k-titi+1Dk,sGlds}],

where the divergence formula (2.3) is applied. Then we can directly obtain the integration by parts using the inverse of V() (without using the inverse of A()). We get the following simple weights.

Corollary D.1.

When N=d, Theorem B.1 holds for i=0,1,,n-1 with

ϑti+1ti,x=1+j1,j2=0dj3,j4=1d12hLj1Vj2j4(x)(V-1)j3j4(x)𝕎(j1,j2,j3)(ti,ti+1)+j1,,j6=1d14Lj1Vj2j4(x)Lj1Vj2j6(x)(V-1)j3j4(x)(V-1)j5j6𝕎(j3,j5)(ti,ti+1).

Proof.

Apply formula (D.1) to the proof of Theorem B.1. ∎

Corollary D.2.

When N=d, Theorem B.2 holds for i=0,1,,n-1 with

ϱti+1ti,x,k={Wti,ti+1kh+l,p=1di1,i2=0d1hLi1Vi2p(x)(V-1)lp(x)
   ×{2h(𝕎(i1,i2,k,l)(ti,ti+1)+𝕎(0,i2,l)(ti,ti+1)𝟏{i1=k0}+𝕎(0,i1,l)(ti,ti+1)𝟏{i2=k0})
      -12h2(3𝕎(i1,i2,0,k,l)(ti,ti+1)
         +2𝕎(0,0,i2,l)(ti,ti+1)𝟏{i1=h0}+4𝕎(i1,0,0,l)(ti,ti+1)𝟏{i2=k0})}
+l,p=1di1,i2,i3=0d1hLi1Li2Vi3p(x)(V-1)lp(x)
   ×{23h(𝕎(0,i2,i3,l)(ti,ti+1)𝟏{i1=k0}+𝕎(i1,0,i3,l)𝟏{i2=k0}+𝕎(i1,i2,0,l)(ti,ti+1)𝟏{i3=k0})
      -14h2(𝕎(0,0,i2,i3,l)(ti,ti+1)𝟏{i1=k0}
         +2𝕎(i1,0,0,i3,l)(ti,ti+1)𝟏{i2=k0}+𝕎(i1,i2,0,0,l)(ti,ti+1)𝟏{k=i30})}
+l,m,p1,p2=1di1,j1,i2,j2=0d12Li1Vi2(x)Lj1Vj2(x)1h2(V-1)lp1(x)(V-1)mp2(x)
   ×{23h(𝕎(0,0,i2,l,m)(ti,ti+1)(2𝟏{j1=i10}𝟏{k=j20}+𝟏{j1=k0}𝟏{i1=j20})
         +𝕎(0,0,j2,l,m)(ti,ti+1)(2𝟏{i1=j10}𝟏{k=i20}+𝟏{i1=k0}𝟏{j1=i20})
         +3𝕎(0,k,0,l,m)(ti,ti+1)𝟏{i1=j10}𝟏{i2=j20}
         +𝕎(0,j1,0,l,m)(ti,ti+1)(2𝟏{i1=k0}𝟏{i2=j20}+𝟏{i1=j20}𝟏{i2=k0})
         +𝕎(0,i1,0,l,m)(ti,ti+1)(2𝟏{j1=k0}𝟏{i2=j20}+𝟏{j1=i20}𝟏{j2=k0}))
      -14h2(6𝕎(0,0,0,k,l,m)(ti,ti+1)𝟏{i1=j10}𝟏{i2=j20}
         +𝕎(0,0,0,j2,l,m)(ti,ti+1)(5𝟏{i1=j10}𝟏{i2=k0}+𝟏{i1=k0}𝟏{i2=j10})
         +𝕎(0,0,0,i2,l,m)(ti,ti+1)(5𝟏{j1=i10}𝟏{k=j20}+𝟏{j1=h0}𝟏{j2=i10})
         +𝕎(i1,0,0,0,l,m)(ti,ti+1)(3𝟏{j1=i20}𝟏{j2=k0}+3𝟏{j1=h0}𝟏{i2=j20})
         +𝕎(j1,0,0,0,l,m)(ti,ti+1)(3𝟏{i1=j20}𝟏{i2=k0}+3𝟏{i1=k0}𝟏{i2=j20}))}
+l,m,p1,p2=1di1,i2,i3,j1,j2=0dLi1Li2Vi3p1(x)Lj1Vj2p2(x)(V-1)lp1(x)(V-1)mp2(x)
   ×{23𝕎(l,m)(ti,ti+1)(𝟏{i1=j10}𝟏{i2=j20}𝟏{i3=k0}
         +𝟏{i1=j10}𝟏{i2=k0}𝟏{i3=j20}+𝟏{i1=k0}𝟏{i2=j10}𝟏{i3=j20})
      -14𝕎(l,m)(ti,ti+1)(3𝟏{i1=j10}𝟏{i2=j20}𝟏{i3=k0}
         +2𝟏{i1=j10}𝟏{i2=k0}𝟏{i3=j20}+𝟏{i1=k0}𝟏{i2=j10}𝟏{i3=j20})}}.

Proof.

Apply formula (D.1) to the proof of Theorem B.2.∎

Remark D.3.

Here, 𝕎(i1,i2,i3,i4)(ti,ti+1), ij{0,1,,d}, j=1,,4 appeared in Theorem B.2 and Corollary D.2 are explicitly obtained by

𝕎(i1,i2,i3,i4)(ti,ti+1):-Wti1Wti2Wti3Wi4-hWti1Wti4𝟏{i2=i30}-hWti1Wti3𝟏{i2=i40}-hWti1Wti2𝟏{i3=i40}-hWti2Wti3𝟏{i1=i40}-hWti2Wti4𝟏{i1=i30}-hWti3Wti4𝟏{i1=i20}+h2𝟏{i3=i40}𝟏{i1=i20}+h2𝟏{i1=i40}𝟏{i2=i30}+h2𝟏{i2=i40}𝟏{i1=i30}.

We also have

𝕎(i1,i2,i3,i4,0)(ti,ti+1)=h𝕎(i1,i2,i3,i4)(ti,ti+1),
𝕎(0,i1,i2,i3,i4)(ti,ti+1)=𝕎(i1,0,i2,i3,i4)(ti,ti+1)=𝕎(i1,i2,0,i3,i4)(ti,ti+1)=𝕎(i1,i2,i3,0,i4)(ti,ti+1)=𝕎(i1,i2,i3,i4,0)(ti,ti+1).

Furthermore, we have

𝕎(i1,i2,i3,0,0,0)(ti,ti+1)=h𝕎(i1,i2,i3,0,0)(ti,ti+1),
𝕎(0,0,0,i1,i2,i3)(ti,ti+1)=𝕎(0,0,i1,0,i2,i3)(ti,ti+1)=𝕎(0,0,i1,i2,0,i3)(ti,ti+1)=𝕎(0,0,i1,i2,i3,0)(ti,ti+1)=𝕎(0,i1,0,0,i2,i3)(ti,ti+1)=𝕎(0,i1,0,i2,0,i3)(ti,ti+1)=𝕎(0,i1,0,i2,i3,0)(ti,ti+1)=𝕎(0,i1,i2,0,0,i3)(ti,ti+1)=𝕎(0,i1,i2,0,i3,0)(ti,ti+1)=𝕎(0,i1,i2,i3,0,0)(ti,ti+1)=𝕎(i1,0,0,0,i2,i3)(ti,ti+1)=𝕎(i1,0,0,i2,0,i3)(ti,ti+1)=𝕎(i1,0,0,i2,i3,0)(ti,ti+1)=𝕎(i1,0,i2,0,0,i3)(ti,ti+1)=𝕎(i1,0,i2,0,i3,0)(ti,ti+1)=𝕎(i1,0,i2,i3,0,0)(ti,ti+1)=𝕎(i1,i2,0,0,0,i3)(ti,ti+1)=𝕎(i1,i2,0,0,i3,0)(ti,ti+1)=𝕎(i1,i2,0,i3,0,0)(ti,ti+1)=𝕎(i1,i2,i3,0,0,0)(ti,ti+1).

Corollary D.4.

The following holds with the weights ϑti+1ti,x in Corollary D.1 and ϱti+1ti,x,k, k=1,,d in Corollary D.2(i=0,1,,n-1):

|Y0-Y0Mall|=O(1n2).

Proof.

Apply Corollary D.1 and Corollary D.2 to the proof of Theorem 2.4. ∎

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Received: 2019-07-03
Revised: 2019-10-15
Accepted: 2019-10-23
Published Online: 2019-11-23
Published in Print: 2019-12-01

© 2019 Walter de Gruyter GmbH, Berlin/Boston

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