Actual source code: ex11.c
2: static char help[] = "Solves a linear system in parallel with KSP.\n\n";
4: /*
5: Description: Solves a complex linear system in parallel with KSP.
7: The model problem:
8: Solve Helmholtz equation on the unit square: (0,1) x (0,1)
9: -delta u - sigma1*u + i*sigma2*u = f,
10: where delta = Laplace operator
11: Dirichlet b.c.'s on all sides
12: Use the 2-D, five-point finite difference stencil.
14: Compiling the code:
15: This code uses the complex numbers version of PETSc, so configure
16: must be run to enable this
17: */
19: /*
20: Include "petscksp.h" so that we can use KSP solvers. Note that this file
21: automatically includes:
22: petscsys.h - base PETSc routines petscvec.h - vectors
23: petscmat.h - matrices
24: petscis.h - index sets petscksp.h - Krylov subspace methods
25: petscviewer.h - viewers petscpc.h - preconditioners
26: */
27: #include <petscksp.h>
29: int main(int argc, char **args)
30: {
31: Vec x, b, u; /* approx solution, RHS, exact solution */
32: Mat A; /* linear system matrix */
33: KSP ksp; /* linear solver context */
34: PetscReal norm; /* norm of solution error */
35: PetscInt dim, i, j, Ii, J, Istart, Iend, n = 6, its, use_random;
36: PetscScalar v, none = -1.0, sigma2, pfive = 0.5, *xa;
37: PetscRandom rctx;
38: PetscReal h2, sigma1 = 100.0;
39: PetscBool flg = PETSC_FALSE;
41: PetscFunctionBeginUser;
42: PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
43: PetscCall(PetscOptionsGetReal(NULL, NULL, "-sigma1", &sigma1, NULL));
44: PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));
45: dim = n * n;
47: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
48: Compute the matrix and right-hand-side vector that define
49: the linear system, Ax = b.
50: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
51: /*
52: Create parallel matrix, specifying only its global dimensions.
53: When using MatCreate(), the matrix format can be specified at
54: runtime. Also, the parallel partitioning of the matrix is
55: determined by PETSc at runtime.
56: */
57: PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
58: PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, dim, dim));
59: PetscCall(MatSetFromOptions(A));
60: PetscCall(MatSetUp(A));
62: /*
63: Currently, all PETSc parallel matrix formats are partitioned by
64: contiguous chunks of rows across the processors. Determine which
65: rows of the matrix are locally owned.
66: */
67: PetscCall(MatGetOwnershipRange(A, &Istart, &Iend));
69: /*
70: Set matrix elements in parallel.
71: - Each processor needs to insert only elements that it owns
72: locally (but any non-local elements will be sent to the
73: appropriate processor during matrix assembly).
74: - Always specify global rows and columns of matrix entries.
75: */
77: PetscCall(PetscOptionsGetBool(NULL, NULL, "-norandom", &flg, NULL));
78: if (flg) use_random = 0;
79: else use_random = 1;
80: if (use_random) {
81: PetscCall(PetscRandomCreate(PETSC_COMM_WORLD, &rctx));
82: PetscCall(PetscRandomSetFromOptions(rctx));
83: PetscCall(PetscRandomSetInterval(rctx, 0.0, PETSC_i));
84: } else {
85: sigma2 = 10.0 * PETSC_i;
86: }
87: h2 = 1.0 / ((n + 1) * (n + 1));
88: for (Ii = Istart; Ii < Iend; Ii++) {
89: v = -1.0;
90: i = Ii / n;
91: j = Ii - i * n;
92: if (i > 0) {
93: J = Ii - n;
94: PetscCall(MatSetValues(A, 1, &Ii, 1, &J, &v, ADD_VALUES));
95: }
96: if (i < n - 1) {
97: J = Ii + n;
98: PetscCall(MatSetValues(A, 1, &Ii, 1, &J, &v, ADD_VALUES));
99: }
100: if (j > 0) {
101: J = Ii - 1;
102: PetscCall(MatSetValues(A, 1, &Ii, 1, &J, &v, ADD_VALUES));
103: }
104: if (j < n - 1) {
105: J = Ii + 1;
106: PetscCall(MatSetValues(A, 1, &Ii, 1, &J, &v, ADD_VALUES));
107: }
108: if (use_random) PetscCall(PetscRandomGetValue(rctx, &sigma2));
109: v = 4.0 - sigma1 * h2 + sigma2 * h2;
110: PetscCall(MatSetValues(A, 1, &Ii, 1, &Ii, &v, ADD_VALUES));
111: }
112: if (use_random) PetscCall(PetscRandomDestroy(&rctx));
114: /*
115: Assemble matrix, using the 2-step process:
116: MatAssemblyBegin(), MatAssemblyEnd()
117: Computations can be done while messages are in transition
118: by placing code between these two statements.
119: */
120: PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
121: PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
123: /*
124: Create parallel vectors.
125: - When using VecCreate(), VecSetSizes() and VecSetFromOptions(),
126: we specify only the vector's global
127: dimension; the parallel partitioning is determined at runtime.
128: - Note: We form 1 vector from scratch and then duplicate as needed.
129: */
130: PetscCall(VecCreate(PETSC_COMM_WORLD, &u));
131: PetscCall(VecSetSizes(u, PETSC_DECIDE, dim));
132: PetscCall(VecSetFromOptions(u));
133: PetscCall(VecDuplicate(u, &b));
134: PetscCall(VecDuplicate(b, &x));
136: /*
137: Set exact solution; then compute right-hand-side vector.
138: */
140: if (use_random) {
141: PetscCall(PetscRandomCreate(PETSC_COMM_WORLD, &rctx));
142: PetscCall(PetscRandomSetFromOptions(rctx));
143: PetscCall(VecSetRandom(u, rctx));
144: } else {
145: PetscCall(VecSet(u, pfive));
146: }
147: PetscCall(MatMult(A, u, b));
149: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
150: Create the linear solver and set various options
151: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
153: /*
154: Create linear solver context
155: */
156: PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
158: /*
159: Set operators. Here the matrix that defines the linear system
160: also serves as the preconditioning matrix.
161: */
162: PetscCall(KSPSetOperators(ksp, A, A));
164: /*
165: Set runtime options, e.g.,
166: -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
167: */
168: PetscCall(KSPSetFromOptions(ksp));
170: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
171: Solve the linear system
172: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
174: PetscCall(KSPSolve(ksp, b, x));
176: /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
177: Check solution and clean up
178: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
180: /*
181: Print the first 3 entries of x; this demonstrates extraction of the
182: real and imaginary components of the complex vector, x.
183: */
184: flg = PETSC_FALSE;
185: PetscCall(PetscOptionsGetBool(NULL, NULL, "-print_x3", &flg, NULL));
186: if (flg) {
187: PetscCall(VecGetArray(x, &xa));
188: PetscCall(PetscPrintf(PETSC_COMM_WORLD, "The first three entries of x are:\n"));
189: for (i = 0; i < 3; i++) PetscCall(PetscPrintf(PETSC_COMM_WORLD, "x[%" PetscInt_FMT "] = %g + %g i\n", i, (double)PetscRealPart(xa[i]), (double)PetscImaginaryPart(xa[i])));
190: PetscCall(VecRestoreArray(x, &xa));
191: }
193: /*
194: Check the error
195: */
196: PetscCall(VecAXPY(x, none, u));
197: PetscCall(VecNorm(x, NORM_2, &norm));
198: PetscCall(KSPGetIterationNumber(ksp, &its));
199: if (norm < 1.e-12) {
200: PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Norm of error < 1.e-12 iterations %" PetscInt_FMT "\n", its));
201: } else {
202: PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Norm of error %g iterations %" PetscInt_FMT "\n", (double)norm, its));
203: }
205: /*
206: Free work space. All PETSc objects should be destroyed when they
207: are no longer needed.
208: */
209: PetscCall(KSPDestroy(&ksp));
210: if (use_random) PetscCall(PetscRandomDestroy(&rctx));
211: PetscCall(VecDestroy(&u));
212: PetscCall(VecDestroy(&x));
213: PetscCall(VecDestroy(&b));
214: PetscCall(MatDestroy(&A));
215: PetscCall(PetscFinalize());
216: return 0;
217: }
219: /*TEST
221: build:
222: requires: complex
224: test:
225: args: -n 6 -norandom -pc_type none -ksp_monitor_short -ksp_gmres_cgs_refinement_type refine_always
227: testset:
228: suffix: deflation
229: args: -norandom -pc_type deflation -ksp_monitor_short
230: requires: superlu_dist
232: test:
233: nsize: 6
235: test:
236: nsize: 3
237: args: -pc_deflation_compute_space {{db2 aggregation}}
239: test:
240: suffix: pc_deflation_init_only-0
241: nsize: 4
242: args: -ksp_type fgmres -pc_deflation_compute_space db4 -pc_deflation_compute_space_size 2 -pc_deflation_levels 2 -deflation_ksp_max_it 10
243: #TODO remove suffix and next test when this works
244: #args: -pc_deflation_init_only {{0 1}separate output}
245: args: -pc_deflation_init_only 0
247: test:
248: suffix: pc_deflation_init_only-1
249: nsize: 4
250: args: -ksp_type fgmres -pc_deflation_compute_space db4 -pc_deflation_compute_space_size 2 -pc_deflation_levels 2 -deflation_ksp_max_it 10
251: args: -pc_deflation_init_only 1
253: TEST*/