Actual source code: fbcgsr.c
petsc-3.6.1 2015-08-06
2: /*
3: This file implements FBiCGStab-R.
4: Only allow right preconditioning.
5: FBiCGStab-R is a mathematically equivalent variant of FBiCGStab. Differences are:
6: (1) There are fewer MPI_Allreduce calls.
7: (2) The convergence occasionally is much faster than that of FBiCGStab.
8: */
9: #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h> /*I "petscksp.h" I*/
10: #include <petsc/private/vecimpl.h>
14: PetscErrorCode KSPSetUp_FBCGSR(KSP ksp)
15: {
19: KSPSetWorkVecs(ksp,8);
20: return(0);
21: }
23: #include <petsc/private/pcimpl.h> /*I "petscksp.h" I*/
26: PetscErrorCode KSPSolve_FBCGSR(KSP ksp)
27: {
28: PetscErrorCode ierr;
29: PetscInt i,j,N;
30: PetscScalar tau,sigma,alpha,omega,beta;
31: PetscReal rho;
32: PetscScalar xi1,xi2,xi3,xi4;
33: Vec X,B,P,P2,RP,R,V,S,T,S2;
34: PetscScalar *PETSC_RESTRICT rp, *PETSC_RESTRICT r, *PETSC_RESTRICT p;
35: PetscScalar *PETSC_RESTRICT v, *PETSC_RESTRICT s, *PETSC_RESTRICT t, *PETSC_RESTRICT s2;
36: PetscScalar insums[4],outsums[4];
37: KSP_BCGS *bcgs = (KSP_BCGS*)ksp->data;
38: PC pc;
41: if (!ksp->vec_rhs->petscnative) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Only coded for PETSc vectors");
42: VecGetLocalSize(ksp->vec_sol,&N);
44: X = ksp->vec_sol;
45: B = ksp->vec_rhs;
46: P2 = ksp->work[0];
48: /* The followings are involved in modified inner product calculations and vector updates */
49: RP = ksp->work[1]; VecGetArray(RP,(PetscScalar**)&rp); VecRestoreArray(RP,NULL);
50: R = ksp->work[2]; VecGetArray(R,(PetscScalar**)&r); VecRestoreArray(R,NULL);
51: P = ksp->work[3]; VecGetArray(P,(PetscScalar**)&p); VecRestoreArray(P,NULL);
52: V = ksp->work[4]; VecGetArray(V,(PetscScalar**)&v); VecRestoreArray(V,NULL);
53: S = ksp->work[5]; VecGetArray(S,(PetscScalar**)&s); VecRestoreArray(S,NULL);
54: T = ksp->work[6]; VecGetArray(T,(PetscScalar**)&t); VecRestoreArray(T,NULL);
55: S2 = ksp->work[7]; VecGetArray(S2,(PetscScalar**)&s2); VecRestoreArray(S2,NULL);
57: /* Only supports right preconditioning */
58: if (ksp->pc_side != PC_RIGHT) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSP fbcgsr does not support %s",PCSides[ksp->pc_side]);
59: if (!ksp->guess_zero) {
60: if (!bcgs->guess) {
61: VecDuplicate(X,&bcgs->guess);
62: }
63: VecCopy(X,bcgs->guess);
64: } else {
65: VecSet(X,0.0);
66: }
68: /* Compute initial residual */
69: KSPGetPC(ksp,&pc);
70: PCSetUp(pc);
71: if (!ksp->guess_zero) {
72: KSP_MatMult(ksp,pc->mat,X,P2); /* P2 is used as temporary storage */
73: VecCopy(B,R);
74: VecAXPY(R,-1.0,P2);
75: } else {
76: VecCopy(B,R);
77: }
79: /* Test for nothing to do */
80: if (ksp->normtype != KSP_NORM_NONE) {
81: VecNorm(R,NORM_2,&rho);
82: }
83: PetscObjectSAWsTakeAccess((PetscObject)ksp);
84: ksp->its = 0;
85: ksp->rnorm = rho;
86: PetscObjectSAWsGrantAccess((PetscObject)ksp);
87: KSPLogResidualHistory(ksp,rho);
88: KSPMonitor(ksp,0,rho);
89: (*ksp->converged)(ksp,0,rho,&ksp->reason,ksp->cnvP);
90: if (ksp->reason) return(0);
92: /* Initialize iterates */
93: VecCopy(R,RP); /* rp <- r */
94: VecCopy(R,P); /* p <- r */
96: /* Big loop */
97: for (i=0; i<ksp->max_it; i++) {
99: /* matmult and pc */
100: KSP_PCApply(ksp,P,P2); /* p2 <- K p */
101: KSP_MatMult(ksp,pc->mat,P2,V); /* v <- A p2 */
103: /* inner prodcuts */
104: if (i==0) {
105: tau = rho*rho;
106: VecDot(V,RP,&sigma); /* sigma <- (v,rp) */
107: } else {
108: PetscLogEventBegin(VEC_ReduceArithmetic,0,0,0,0);
109: tau = sigma = 0.0;
110: for (j=0; j<N; j++) {
111: tau += r[j]*rp[j]; /* tau <- (r,rp) */
112: sigma += v[j]*rp[j]; /* sigma <- (v,rp) */
113: }
114: PetscLogFlops(4.0*N);
115: PetscLogEventEnd(VEC_ReduceArithmetic,0,0,0,0);
116: insums[0] = tau;
117: insums[1] = sigma;
118: PetscLogEventBarrierBegin(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
119: MPI_Allreduce(insums,outsums,2,MPIU_SCALAR,MPIU_SUM,PetscObjectComm((PetscObject)ksp));
120: PetscLogEventBarrierEnd(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
121: tau = outsums[0];
122: sigma = outsums[1];
123: }
125: /* scalar update */
126: alpha = tau / sigma;
128: /* vector update */
129: VecWAXPY(S,-alpha,V,R); /* s <- r - alpha v */
131: /* matmult and pc */
132: KSP_PCApply(ksp,S,S2); /* s2 <- K s */
133: KSP_MatMult(ksp,pc->mat,S2,T); /* t <- A s2 */
135: /* inner prodcuts */
136: PetscLogEventBegin(VEC_ReduceArithmetic,0,0,0,0);
137: xi1 = xi2 = xi3 = xi4 = 0.0;
138: for (j=0; j<N; j++) {
139: xi1 += s[j]*s[j]; /* xi1 <- (s,s) */
140: xi2 += t[j]*s[j]; /* xi2 <- (t,s) */
141: xi3 += t[j]*t[j]; /* xi3 <- (t,t) */
142: xi4 += t[j]*rp[j]; /* xi4 <- (t,rp) */
143: }
144: PetscLogFlops(8.0*N);
145: PetscLogEventEnd(VEC_ReduceArithmetic,0,0,0,0);
147: insums[0] = xi1;
148: insums[1] = xi2;
149: insums[2] = xi3;
150: insums[3] = xi4;
152: PetscLogEventBarrierBegin(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
153: MPI_Allreduce(insums,outsums,4,MPIU_SCALAR,MPIU_SUM,PetscObjectComm((PetscObject)ksp));
154: PetscLogEventBarrierEnd(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
155: xi1 = outsums[0];
156: xi2 = outsums[1];
157: xi3 = outsums[2];
158: xi4 = outsums[3];
160: /* test denominator */
161: if (xi3 == 0.0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_PLIB,"Divide by zero");
162: if (sigma == 0.0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_PLIB,"Divide by zero");
164: /* scalar updates */
165: omega = xi2 / xi3;
166: beta = -xi4 / sigma;
167: rho = PetscSqrtReal(PetscAbsScalar(xi1 - omega * xi2)); /* residual norm */
169: /* vector updates */
170: VecAXPBYPCZ(X,alpha,omega,1.0,P2,S2); /* x <- alpha * p2 + omega * s2 + x */
172: /* convergence test */
173: PetscObjectSAWsTakeAccess((PetscObject)ksp);
174: ksp->its++;
175: ksp->rnorm = rho;
176: PetscObjectSAWsGrantAccess((PetscObject)ksp);
177: KSPLogResidualHistory(ksp,rho);
178: KSPMonitor(ksp,i+1,rho);
179: (*ksp->converged)(ksp,i+1,rho,&ksp->reason,ksp->cnvP);
180: if (ksp->reason) break;
182: /* vector updates */
183: PetscLogEventBegin(VEC_Ops,0,0,0,0);
184: for (j=0; j<N; j++) {
185: r[j] = s[j] - omega * t[j]; /* r <- s - omega t */
186: p[j] = r[j] + beta * (p[j] - omega * v[j]); /* p <- r + beta * (p - omega v) */
187: }
188: PetscLogFlops(6.0*N);
189: PetscLogEventEnd(VEC_Ops,0,0,0,0);
191: }
193: if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
194: return(0);
195: }
197: /*MC
198: KSPFBCGSR - Implements a mathematically equivalent variant of FBiCGSTab.
200: Options Database Keys:
201: . see KSPSolve()
203: Level: beginner
205: Notes: Only allow right preconditioning
207: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPFBCGSL, KSPSetPCSide()
208: M*/
211: PETSC_EXTERN PetscErrorCode KSPCreate_FBCGSR(KSP ksp)
212: {
214: KSP_BCGS *bcgs;
217: PetscNewLog(ksp,&bcgs);
219: ksp->data = bcgs;
220: ksp->ops->setup = KSPSetUp_FBCGSR;
221: ksp->ops->solve = KSPSolve_FBCGSR;
222: ksp->ops->destroy = KSPDestroy_BCGS;
223: ksp->ops->reset = KSPReset_BCGS;
224: ksp->ops->buildsolution = KSPBuildSolution_BCGS;
225: ksp->ops->buildresidual = KSPBuildResidualDefault;
226: ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;
227: ksp->pc_side = PC_RIGHT; /* set default PC side */
229: KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
230: KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
231: return(0);
232: }