Date: 2022-08-02T03:15:06+00:00

Actual source code: ex5.c

      2: static char help[] = "Demonstrates Pattern Formation with Reaction-Diffusion Equations.\n";

This example is taken from the book, Numerical Solution of Time-Dependent Advection-Diffusion-Reaction Equations by
W. Hundsdorf and J.G. Verwer, Page 21, Pattern Formation with Reaction-Diffusion Equations
\begin{eqnarray*}
u_t = D_1 (u_{xx} + u_{yy}) - u*v^2 + \gamma(1 -u) \\
v_t = D_2 (v_{xx} + v_{yy}) + u*v^2 - (\gamma + \kappa)v
\end{eqnarray*}
Unlike in the book this uses periodic boundary conditions instead of Neumann
(since they are easier for finite differences).

     15: /*
     16:       Helpful runtime monitor options:
     17:            -ts_monitor_draw_solution
     18:            -draw_save -draw_save_movie

     20:       Helpful runtime linear solver options:
     21:            -pc_type mg -pc_mg_galerkin pmat -da_refine 1 -snes_monitor -ksp_monitor -ts_view  (note that these Jacobians are so well-conditioned multigrid may not be the best solver)

     23:       Point your browser to localhost:8080 to monitor the simulation
     24:            ./ex5  -ts_view_pre saws  -stack_view saws -draw_save -draw_save_single_file -x_virtual -ts_monitor_draw_solution -saws_root .

     26: */

     28: /*

     30:    Include "petscdmda.h" so that we can use distributed arrays (DMDAs).
     31:    Include "petscts.h" so that we can use SNES numerical (ODE) integrators.  Note that this
     32:    file automatically includes:
     33:      petscsys.h       - base PETSc routines   petscvec.h  - vectors
     34:      petscmat.h - matrices                    petscis.h   - index sets
     35:      petscksp.h - Krylov subspace methods     petscpc.h   - preconditioners
     36:      petscviewer.h - viewers                  petscsnes.h - nonlinear solvers
     37: */
     38: #include "reaction_diffusion.h"
     39: #include <petscdm.h>
     40: #include <petscdmda.h>

     42: /* ------------------------------------------------------------------- */
     43: PetscErrorCode InitialConditions(DM da,Vec U)
     44: {
     45:   PetscInt       i,j,xs,ys,xm,ym,Mx,My;
     46:   Field          **u;
     47:   PetscReal      hx,hy,x,y;

     49:   DMDAGetInfo(da,PETSC_IGNORE,&Mx,&My,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);

     51:   hx = 2.5/(PetscReal)(Mx);
     52:   hy = 2.5/(PetscReal)(My);

     54:   /*
     55:      Get pointers to actual vector data
     56:   */
     57:   DMDAVecGetArray(da,U,&u);

     59:   /*
     60:      Get local grid boundaries
     61:   */
     62:   DMDAGetCorners(da,&xs,&ys,NULL,&xm,&ym,NULL);

     64:   /*
     65:      Compute function over the locally owned part of the grid
     66:   */
     67:   for (j=ys; j<ys+ym; j++) {
     68:     y = j*hy;
     69:     for (i=xs; i<xs+xm; i++) {
     70:       x = i*hx;
     71:       if (PetscApproximateGTE(x,1.0) && PetscApproximateLTE(x,1.5) && PetscApproximateGTE(y,1.0) && PetscApproximateLTE(y,1.5)) u[j][i].v = PetscPowReal(PetscSinReal(4.0*PETSC_PI*x),2.0)*PetscPowReal(PetscSinReal(4.0*PETSC_PI*y),2.0)/4.0;
     72:       else u[j][i].v = 0.0;

     74:       u[j][i].u = 1.0 - 2.0*u[j][i].v;
     75:     }
     76:   }

     78:   /*
     79:      Restore access to vector
     80:   */
     81:   DMDAVecRestoreArray(da,U,&u);
     82:   return 0;
     83: }

     85: int main(int argc,char **argv)
     86: {
     87:   TS     ts;                    /* ODE integrator */
     88:   Vec    x;                     /* solution */
     89:   DM     da;
     90:   AppCtx appctx;

     92:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     93:      Initialize program
     94:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
     95:   PetscInitialize(&argc,&argv,(char*)0,help);
     97:   appctx.D1    = 8.0e-5;
     98:   appctx.D2    = 4.0e-5;
     99:   appctx.gamma = .024;
    100:   appctx.kappa = .06;
    101:   appctx.aijpc = PETSC_FALSE;

    103:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    104:      Create distributed array (DMDA) to manage parallel grid and vectors
    105:   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    106:   DMDACreate2d(PETSC_COMM_WORLD,DM_BOUNDARY_PERIODIC,DM_BOUNDARY_PERIODIC,DMDA_STENCIL_STAR,65,65,PETSC_DECIDE,PETSC_DECIDE,2,1,NULL,NULL,&da);
    107:   DMSetFromOptions(da);
    108:   DMSetUp(da);
    109:   DMDASetFieldName(da,0,"u");
    110:   DMDASetFieldName(da,1,"v");

    112:   /*  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    113:      Create global vector from DMDA; this will be used to store the solution
    114:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    115:   DMCreateGlobalVector(da,&x);

    117:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    118:      Create timestepping solver context
    119:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    120:   TSCreate(PETSC_COMM_WORLD,&ts);
    121:   TSSetType(ts,TSARKIMEX);
    122:   TSARKIMEXSetFullyImplicit(ts,PETSC_TRUE);
    123:   TSSetDM(ts,da);
    124:   TSSetProblemType(ts,TS_NONLINEAR);
    125:   TSSetRHSFunction(ts,NULL,RHSFunction,&appctx);
    126:   TSSetRHSJacobian(ts,NULL,NULL,RHSJacobian,&appctx);

    128:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    129:      Set initial conditions
    130:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    131:   InitialConditions(da,x);
    132:   TSSetSolution(ts,x);

    134:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    135:      Set solver options
    136:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    137:   TSSetMaxTime(ts,2000.0);
    138:   TSSetTimeStep(ts,.0001);
    139:   TSSetExactFinalTime(ts,TS_EXACTFINALTIME_STEPOVER);
    140:   TSSetFromOptions(ts);

    142:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    143:      Solve ODE system
    144:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    145:   TSSolve(ts,x);

    147:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    148:      Free work space.
    149:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    150:   VecDestroy(&x);
    151:   TSDestroy(&ts);
    152:   DMDestroy(&da);

    154:   PetscFinalize();
    155:   return 0;
    156: }

    158: /*TEST

    160:    build:
    161:      depends: reaction_diffusion.c

    163:    test:
    164:       args: -ts_view  -ts_monitor -ts_max_time 500
    165:       requires: double
    166:       timeoutfactor: 3

    168:    test:
    169:       suffix: 2
    170:       args: -ts_view  -ts_monitor -ts_max_time 500 -ts_monitor_draw_solution
    171:       requires: x double
    172:       output_file: output/ex5_1.out
    173:       timeoutfactor: 3

    175: TEST*/