Actual source code: pipecg.c
petsc-3.14.6 2021-03-30
2: #include <petsc/private/kspimpl.h>
4: /*
5: KSPSetUp_PIPECG - Sets up the workspace needed by the PIPECG method.
7: This is called once, usually automatically by KSPSolve() or KSPSetUp()
8: but can be called directly by KSPSetUp()
9: */
10: static PetscErrorCode KSPSetUp_PIPECG(KSP ksp)
11: {
15: /* get work vectors needed by PIPECG */
16: KSPSetWorkVecs(ksp,9);
17: return(0);
18: }
20: /*
21: KSPSolve_PIPECG - This routine actually applies the pipelined conjugate gradient method
22: */
23: static PetscErrorCode KSPSolve_PIPECG(KSP ksp)
24: {
26: PetscInt i;
27: PetscScalar alpha = 0.0,beta = 0.0,gamma = 0.0,gammaold = 0.0,delta = 0.0;
28: PetscReal dp = 0.0;
29: Vec X,B,Z,P,W,Q,U,M,N,R,S;
30: Mat Amat,Pmat;
31: PetscBool diagonalscale;
34: PCGetDiagonalScale(ksp->pc,&diagonalscale);
35: if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
37: X = ksp->vec_sol;
38: B = ksp->vec_rhs;
39: R = ksp->work[0];
40: Z = ksp->work[1];
41: P = ksp->work[2];
42: N = ksp->work[3];
43: W = ksp->work[4];
44: Q = ksp->work[5];
45: U = ksp->work[6];
46: M = ksp->work[7];
47: S = ksp->work[8];
49: PCGetOperators(ksp->pc,&Amat,&Pmat);
51: ksp->its = 0;
52: if (!ksp->guess_zero) {
53: KSP_MatMult(ksp,Amat,X,R); /* r <- b - Ax */
54: VecAYPX(R,-1.0,B);
55: } else {
56: VecCopy(B,R); /* r <- b (x is 0) */
57: }
59: KSP_PCApply(ksp,R,U); /* u <- Br */
61: switch (ksp->normtype) {
62: case KSP_NORM_PRECONDITIONED:
63: VecNormBegin(U,NORM_2,&dp); /* dp <- u'*u = e'*A'*B'*B*A'*e' */
64: PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)U));
65: KSP_MatMult(ksp,Amat,U,W); /* w <- Au */
66: VecNormEnd(U,NORM_2,&dp);
67: break;
68: case KSP_NORM_UNPRECONDITIONED:
69: VecNormBegin(R,NORM_2,&dp); /* dp <- r'*r = e'*A'*A*e */
70: PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)R));
71: KSP_MatMult(ksp,Amat,U,W); /* w <- Au */
72: VecNormEnd(R,NORM_2,&dp);
73: break;
74: case KSP_NORM_NATURAL:
75: VecDotBegin(R,U,&gamma); /* gamma <- u'*r */
76: PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)R));
77: KSP_MatMult(ksp,Amat,U,W); /* w <- Au */
78: VecDotEnd(R,U,&gamma);
79: KSPCheckDot(ksp,gamma);
80: dp = PetscSqrtReal(PetscAbsScalar(gamma)); /* dp <- r'*u = r'*B*r = e'*A'*B*A*e */
81: break;
82: case KSP_NORM_NONE:
83: KSP_MatMult(ksp,Amat,U,W);
84: dp = 0.0;
85: break;
86: default: SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"%s",KSPNormTypes[ksp->normtype]);
87: }
88: KSPLogResidualHistory(ksp,dp);
89: KSPMonitor(ksp,0,dp);
90: ksp->rnorm = dp;
91: (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP); /* test for convergence */
92: if (ksp->reason) return(0);
94: i = 0;
95: do {
96: if (i > 0 && ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
97: VecNormBegin(R,NORM_2,&dp);
98: } else if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
99: VecNormBegin(U,NORM_2,&dp);
100: }
101: if (!(i == 0 && ksp->normtype == KSP_NORM_NATURAL)) {
102: VecDotBegin(R,U,&gamma);
103: }
104: VecDotBegin(W,U,&delta);
105: PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)R));
107: KSP_PCApply(ksp,W,M); /* m <- Bw */
108: KSP_MatMult(ksp,Amat,M,N); /* n <- Am */
110: if (i > 0 && ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
111: VecNormEnd(R,NORM_2,&dp);
112: } else if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
113: VecNormEnd(U,NORM_2,&dp);
114: }
115: if (!(i == 0 && ksp->normtype == KSP_NORM_NATURAL)) {
116: VecDotEnd(R,U,&gamma);
117: }
118: VecDotEnd(W,U,&delta);
120: if (i > 0) {
121: if (ksp->normtype == KSP_NORM_NATURAL) dp = PetscSqrtReal(PetscAbsScalar(gamma));
122: else if (ksp->normtype == KSP_NORM_NONE) dp = 0.0;
124: ksp->rnorm = dp;
125: KSPLogResidualHistory(ksp,dp);
126: KSPMonitor(ksp,i,dp);
127: (*ksp->converged)(ksp,i,dp,&ksp->reason,ksp->cnvP);
128: if (ksp->reason) return(0);
129: }
131: if (i == 0) {
132: alpha = gamma / delta;
133: VecCopy(N,Z); /* z <- n */
134: VecCopy(M,Q); /* q <- m */
135: VecCopy(U,P); /* p <- u */
136: VecCopy(W,S); /* s <- w */
137: } else {
138: beta = gamma / gammaold;
139: alpha = gamma / (delta - beta / alpha * gamma);
140: VecAYPX(Z,beta,N); /* z <- n + beta * z */
141: VecAYPX(Q,beta,M); /* q <- m + beta * q */
142: VecAYPX(P,beta,U); /* p <- u + beta * p */
143: VecAYPX(S,beta,W); /* s <- w + beta * s */
144: }
145: VecAXPY(X, alpha,P); /* x <- x + alpha * p */
146: VecAXPY(U,-alpha,Q); /* u <- u - alpha * q */
147: VecAXPY(W,-alpha,Z); /* w <- w - alpha * z */
148: VecAXPY(R,-alpha,S); /* r <- r - alpha * s */
149: gammaold = gamma;
150: i++;
151: ksp->its = i;
153: /* if (i%50 == 0) { */
154: /* KSP_MatMult(ksp,Amat,X,R); /\* w <- b - Ax *\/ */
155: /* VecAYPX(R,-1.0,B); */
156: /* KSP_PCApply(ksp,R,U); */
157: /* KSP_MatMult(ksp,Amat,U,W); */
158: /* } */
160: } while (i<=ksp->max_it);
161: if (!ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
162: return(0);
163: }
165: PETSC_INTERN PetscErrorCode KSPBuildResidual_CG(KSP,Vec,Vec,Vec*);
167: /*MC
168: KSPPIPECG - Pipelined conjugate gradient method.
170: This method has only a single non-blocking reduction per iteration, compared to 2 blocking for standard CG. The
171: non-blocking reduction is overlapped by the matrix-vector product and preconditioner application.
173: See also KSPPIPECR, where the reduction is only overlapped with the matrix-vector product.
175: Level: intermediate
177: Notes:
178: MPI configuration may be necessary for reductions to make asynchronous progress, which is important for performance of pipelined methods.
179: See the FAQ on the PETSc website for details.
181: Contributed by:
182: Pieter Ghysels, Universiteit Antwerpen, Intel Exascience lab Flanders
184: Reference:
185: P. Ghysels and W. Vanroose, "Hiding global synchronization latency in the preconditioned Conjugate Gradient algorithm",
186: Submitted to Parallel Computing, 2012.
188: .seealso: KSPCreate(), KSPSetType(), KSPPIPECR, KSPGROPPCG, KSPPGMRES, KSPCG, KSPCGUseSingleReduction()
189: M*/
190: PETSC_EXTERN PetscErrorCode KSPCreate_PIPECG(KSP ksp)
191: {
195: KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
196: KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
197: KSPSetSupportedNorm(ksp,KSP_NORM_NATURAL,PC_LEFT,2);
198: KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);
200: ksp->ops->setup = KSPSetUp_PIPECG;
201: ksp->ops->solve = KSPSolve_PIPECG;
202: ksp->ops->destroy = KSPDestroyDefault;
203: ksp->ops->view = NULL;
204: ksp->ops->setfromoptions = NULL;
205: ksp->ops->buildsolution = KSPBuildSolutionDefault;
206: ksp->ops->buildresidual = KSPBuildResidual_CG;
207: return(0);
208: }