Actual source code: ex13.c
1: /*$Id: ex13.c,v 1.33 2001/08/07 21:31:12 bsmith Exp $*/
3: static char help[] = "This program is a replica of ex6.c except that it does 2 solves to avoid paging.\n\
4: This program demonstrates use of the SNES package to solve systems of\n\
5: nonlinear equations in parallel, using 2-dimensional distributed arrays.\n\
6: The 2-dim Bratu (SFI - solid fuel ignition) test problem is used, where\n\
7: analytic formation of the Jacobian is the default. The command line\n\
8: options are:\n\
9: -par <parameter>, where <parameter> indicates the problem's nonlinearity\n\
10: problem SFI: <parameter> = Bratu parameter (0 <= par <= 6.81)\n\
11: -mx <xg>, where <xg> = number of grid points in the x-direction\n\
12: -my <yg>, where <yg> = number of grid points in the y-direction\n\
13: -Nx <npx>, where <npx> = number of processors in the x-direction\n\
14: -Ny <npy>, where <npy> = number of processors in the y-direction\n\n";
16: /*
17: 1) Solid Fuel Ignition (SFI) problem. This problem is modeled by
18: the partial differential equation
19:
20: -Laplacian u - lambda*exp(u) = 0, 0 < x,y < 1,
21:
22: with boundary conditions
23:
24: u = 0 for x = 0, x = 1, y = 0, y = 1.
25:
26: A finite difference approximation with the usual 5-point stencil
27: is used to discretize the boundary value problem to obtain a nonlinear
28: system of equations.
29: */
31: #include petscsnes.h
32: #include petscda.h
34: /* User-defined application context */
35: typedef struct {
36: PetscReal param; /* test problem parameter */
37: int mx,my; /* discretization in x, y directions */
38: Vec localX,localF; /* ghosted local vector */
39: DA da; /* distributed array data structure */
40: } AppCtx;
42: extern int FormFunction1(SNES,Vec,Vec,void*),FormInitialGuess1(AppCtx*,Vec);
43: extern int FormJacobian1(SNES,Vec,Mat*,Mat*,MatStructure*,void*);
47: int main(int argc,char **argv)
48: {
49: SNES snes; /* nonlinear solver */
50: SNESType type = SNESLS; /* nonlinear solution method */
51: Vec x,r; /* solution, residual vectors */
52: Mat J; /* Jacobian matrix */
53: AppCtx user; /* user-defined work context */
54: int i,ierr,its,N,Nx = PETSC_DECIDE,Ny = PETSC_DECIDE;
55: PetscTruth matrix_free;
56: int size;
57: PetscReal bratu_lambda_max = 6.81,bratu_lambda_min = 0.;
59: PetscInitialize(&argc,&argv,(char *)0,help);
61: for (i=0; i<2; i++) {
62: PetscLogStagePush(i);
63: user.mx = 4; user.my = 4; user.param = 6.0;
64:
65: if (i!=0) {
66: PetscOptionsGetInt(PETSC_NULL,"-mx",&user.mx,PETSC_NULL);
67: PetscOptionsGetInt(PETSC_NULL,"-my",&user.my,PETSC_NULL);
68: PetscOptionsGetReal(PETSC_NULL,"-par",&user.param,PETSC_NULL);
69: if (user.param >= bratu_lambda_max || user.param <= bratu_lambda_min) {
70: SETERRQ(1,"Lambda is out of range");
71: }
72: }
73: N = user.mx*user.my;
75: MPI_Comm_size(PETSC_COMM_WORLD,&size);
76: PetscOptionsGetInt(PETSC_NULL,"-Nx",&Nx,PETSC_NULL);
77: PetscOptionsGetInt(PETSC_NULL,"-Ny",&Ny,PETSC_NULL);
78: if (Nx*Ny != size && (Nx != PETSC_DECIDE || Ny != PETSC_DECIDE))
79: SETERRQ(1,"Incompatible number of processors: Nx * Ny != size");
80:
81: /* Set up distributed array */
82: DACreate2d(PETSC_COMM_WORLD,DA_NONPERIODIC,DA_STENCIL_STAR,user.mx,user.my,Nx,Ny,1,1,
83: PETSC_NULL,PETSC_NULL,&user.da);
84: DACreateGlobalVector(user.da,&x);
85: VecDuplicate(x,&r);
86: DACreateLocalVector(user.da,&user.localX);
87: VecDuplicate(user.localX,&user.localF);
89: /* Create nonlinear solver and set function evaluation routine */
90: SNESCreate(PETSC_COMM_WORLD,&snes);
91: SNESSetType(snes,type);
92: SNESSetFunction(snes,r,FormFunction1,&user);
94: /* Set default Jacobian evaluation routine. User can override with:
95: -snes_mf : matrix-free Newton-Krylov method with no preconditioning
96: (unless user explicitly sets preconditioner)
97: -snes_fd : default finite differencing approximation of Jacobian
98: */
99: PetscOptionsHasName(PETSC_NULL,"-snes_mf",&matrix_free);
100: if (!matrix_free) {
101: MatCreate(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,N,N,&J);
102: MatSetFromOptions(J);
103: SNESSetJacobian(snes,J,J,FormJacobian1,&user);
104: }
106: /* Set PetscOptions, then solve nonlinear system */
107: SNESSetFromOptions(snes);
108: FormInitialGuess1(&user,x);
109: SNESSolve(snes,x,&its);
110: PetscPrintf(PETSC_COMM_WORLD,"Number of Newton iterations = %d\n",its);
112: /* Free data structures */
113: if (!matrix_free) {
114: MatDestroy(J);
115: }
116: VecDestroy(x);
117: VecDestroy(r);
118: VecDestroy(user.localX);
119: VecDestroy(user.localF);
120: SNESDestroy(snes);
121: DADestroy(user.da);
122: }
123: PetscFinalize();
125: return 0;
126: }/* -------------------- Form initial approximation ----------------- */
129: int FormInitialGuess1(AppCtx *user,Vec X)
130: {
131: int i,j,row,mx,my,ierr,xs,ys,xm,ym,Xm,Ym,Xs,Ys;
132: PetscReal one = 1.0,lambda,temp1,temp,hx,hy;
133: PetscScalar *x;
134: Vec localX = user->localX;
136: mx = user->mx; my = user->my; lambda = user->param;
137: hx = one/(PetscReal)(mx-1); hy = one/(PetscReal)(my-1);
139: /* Get ghost points */
140: VecGetArray(localX,&x);
141: temp1 = lambda/(lambda + one);
142: DAGetCorners(user->da,&xs,&ys,0,&xm,&ym,0);
143: DAGetGhostCorners(user->da,&Xs,&Ys,0,&Xm,&Ym,0);
145: /* Compute initial guess */
146: for (j=ys; j<ys+ym; j++) {
147: temp = (PetscReal)(PetscMin(j,my-j-1))*hy;
148: for (i=xs; i<xs+xm; i++) {
149: row = i - Xs + (j - Ys)*Xm;
150: if (i == 0 || j == 0 || i == mx-1 || j == my-1) {
151: x[row] = 0.0;
152: continue;
153: }
154: x[row] = temp1*sqrt(PetscMin((PetscReal)(PetscMin(i,mx-i-1))*hx,temp));
155: }
156: }
157: VecRestoreArray(localX,&x);
159: /* Insert values into global vector */
160: DALocalToGlobal(user->da,localX,INSERT_VALUES,X);
161: return 0;
162: } /* -------------------- Evaluate Function F(x) --------------------- */
165: int FormFunction1(SNES snes,Vec X,Vec F,void *ptr)
166: {
167: AppCtx *user = (AppCtx*)ptr;
168: int ierr,i,j,row,mx,my,xs,ys,xm,ym,Xs,Ys,Xm,Ym;
169: PetscReal two = 2.0,one = 1.0,lambda,hx,hy,hxdhy,hydhx,sc;
170: PetscScalar u,uxx,uyy,*x,*f;
171: Vec localX = user->localX,localF = user->localF;
173: mx = user->mx; my = user->my; lambda = user->param;
174: hx = one/(PetscReal)(mx-1); hy = one/(PetscReal)(my-1);
175: sc = hx*hy*lambda; hxdhy = hx/hy; hydhx = hy/hx;
177: /* Get ghost points */
178: DAGlobalToLocalBegin(user->da,X,INSERT_VALUES,localX);
179: DAGlobalToLocalEnd(user->da,X,INSERT_VALUES,localX);
180: VecGetArray(localX,&x);
181: VecGetArray(localF,&f);
182: DAGetCorners(user->da,&xs,&ys,0,&xm,&ym,0);
183: DAGetGhostCorners(user->da,&Xs,&Ys,0,&Xm,&Ym,0);
185: /* Evaluate function */
186: for (j=ys; j<ys+ym; j++) {
187: row = (j - Ys)*Xm + xs - Xs - 1;
188: for (i=xs; i<xs+xm; i++) {
189: row++;
190: if (i == 0 || j == 0 || i == mx-1 || j == my-1) {
191: f[row] = x[row];
192: continue;
193: }
194: u = x[row];
195: uxx = (two*u - x[row-1] - x[row+1])*hydhx;
196: uyy = (two*u - x[row-Xm] - x[row+Xm])*hxdhy;
197: f[row] = uxx + uyy - sc*PetscExpScalar(u);
198: }
199: }
200: VecRestoreArray(localX,&x);
201: VecRestoreArray(localF,&f);
203: /* Insert values into global vector */
204: DALocalToGlobal(user->da,localF,INSERT_VALUES,F);
205: PetscLogFlops(11*ym*xm);
206: return 0;
207: } /* -------------------- Evaluate Jacobian F'(x) --------------------- */
210: int FormJacobian1(SNES snes,Vec X,Mat *J,Mat *B,MatStructure *flag,void *ptr)
211: {
212: AppCtx *user = (AppCtx*)ptr;
213: Mat jac = *J;
214: int ierr,i,j,row,mx,my,xs,ys,xm,ym,Xs,Ys,Xm,Ym,col[5];
215: int nloc,*ltog,grow;
216: PetscScalar two = 2.0,one = 1.0,lambda,v[5],hx,hy,hxdhy,hydhx,sc,*x;
217: Vec localX = user->localX;
219: mx = user->mx; my = user->my; lambda = user->param;
220: hx = one/(PetscReal)(mx-1); hy = one/(PetscReal)(my-1);
221: sc = hx*hy; hxdhy = hx/hy; hydhx = hy/hx;
223: /* Get ghost points */
224: DAGlobalToLocalBegin(user->da,X,INSERT_VALUES,localX);
225: DAGlobalToLocalEnd(user->da,X,INSERT_VALUES,localX);
226: VecGetArray(localX,&x);
227: DAGetCorners(user->da,&xs,&ys,0,&xm,&ym,0);
228: DAGetGhostCorners(user->da,&Xs,&Ys,0,&Xm,&Ym,0);
229: DAGetGlobalIndices(user->da,&nloc,<og);
231: /* Evaluate function */
232: for (j=ys; j<ys+ym; j++) {
233: row = (j - Ys)*Xm + xs - Xs - 1;
234: for (i=xs; i<xs+xm; i++) {
235: row++;
236: grow = ltog[row];
237: if (i == 0 || j == 0 || i == mx-1 || j == my-1) {
238: MatSetValues(jac,1,&grow,1,&grow,&one,INSERT_VALUES);
239: continue;
240: }
241: v[0] = -hxdhy; col[0] = ltog[row - Xm];
242: v[1] = -hydhx; col[1] = ltog[row - 1];
243: v[2] = two*(hydhx + hxdhy) - sc*lambda*PetscExpScalar(x[row]); col[2] = grow;
244: v[3] = -hydhx; col[3] = ltog[row + 1];
245: v[4] = -hxdhy; col[4] = ltog[row + Xm];
246: MatSetValues(jac,1,&grow,5,col,v,INSERT_VALUES);
247: }
248: }
249: MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
250: VecRestoreArray(X,&x);
251: MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);
252: *flag = SAME_NONZERO_PATTERN;
253: return 0;
254: }