C++ PetscSqrtReal函数代码示例

/*
   Monitor - User-provided routine to monitor the solution computed at
   each timestep.  This example plots the solution and computes the
   error in two different norms.

   Input Parameters:
   ts     - the timestep context
   step   - the count of the current step (with 0 meaning the
            initial condition)
   time   - the current time
   u      - the solution at this timestep
   ctx    - the user-provided context for this monitoring routine.
            In this case we use the application context which contains
            information about the problem size, workspace and the exact
            solution.
*/
PetscErrorCode Monitor(TS ts,PetscInt step,PetscReal time,Vec u,void *ctx)
{
  AppCtx         *appctx = (AppCtx*) ctx;   /* user-defined application context */
  PetscErrorCode ierr;
  PetscReal      en2,en2s,enmax;
  PetscDraw      draw;

  /*
     We use the default X windows viewer
             PETSC_VIEWER_DRAW_(appctx->comm)
     that is associated with the current communicator. This saves
     the effort of calling PetscViewerDrawOpen() to create the window.
     Note that if we wished to plot several items in separate windows we
     would create each viewer with PetscViewerDrawOpen() and store them in
     the application context, appctx.

     PetscReal buffering makes graphics look better.
  */
  ierr = PetscViewerDrawGetDraw(PETSC_VIEWER_DRAW_(appctx->comm),0,&draw);CHKERRQ(ierr);
  ierr = PetscDrawSetDoubleBuffer(draw);CHKERRQ(ierr);
  ierr = VecView(u,PETSC_VIEWER_DRAW_(appctx->comm));CHKERRQ(ierr);

  /*
     Compute the exact solution at this timestep
  */
  ierr = ExactSolution(time,appctx->solution,appctx);CHKERRQ(ierr);

  /*
     Print debugging information if desired
  */
  if (appctx->debug) {
    ierr = PetscPrintf(appctx->comm,"Computed solution vector\n");CHKERRQ(ierr);
    ierr = VecView(u,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
    ierr = PetscPrintf(appctx->comm,"Exact solution vector\n");CHKERRQ(ierr);
    ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  }

  /*
     Compute the 2-norm and max-norm of the error
  */
  ierr = VecAXPY(appctx->solution,-1.0,u);CHKERRQ(ierr);
  ierr = VecNorm(appctx->solution,NORM_2,&en2);CHKERRQ(ierr);
  en2s = PetscSqrtReal(appctx->h)*en2;  /* scale the 2-norm by the grid spacing */
  ierr = VecNorm(appctx->solution,NORM_MAX,&enmax);CHKERRQ(ierr);

  /*
     PetscPrintf() causes only the first processor in this
     communicator to print the timestep information.
  */
  ierr = PetscPrintf(appctx->comm,"Timestep %D: time = %g,2-norm error = %g, max norm error = %g\n",step,(double)time,(double)en2s,(double)enmax);CHKERRQ(ierr);

  /*
     Print debugging information if desired
   */
  /*  if (appctx->debug) {
     ierr = PetscPrintf(appctx->comm,"Error vector\n");CHKERRQ(ierr);
     ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
   } */
  return 0;
}

PetscErrorCode FormInitialGuess(Vec X,AppCtx *user)
{
  PetscInt       i,j,row,mx,my;
  PetscErrorCode ierr;
  PetscReal      one = 1.0,lambda;
  PetscReal      temp1,temp,hx,hy;
  PetscScalar    *x;

  mx	 = user->mx; 
  my	 = user->my;
  lambda = user->param;

  hx    = one / (PetscReal)(mx-1);
  hy    = one / (PetscReal)(my-1);

  ierr = VecGetArray(X,&x);CHKERRQ(ierr);
  temp1 = lambda/(lambda + one);
  for (j=0; j<my; j++) {
    temp = (PetscReal)(PetscMin(j,my-j-1))*hy;
    for (i=0; i<mx; i++) {
      row = i + j*mx;  
      if (i == 0 || j == 0 || i == mx-1 || j == my-1) {
        x[row] = 0.0; 
        continue;
      }
      x[row] = temp1*PetscSqrtReal(PetscMin((PetscReal)(PetscMin(i,mx-i-1))*hx,temp)); 
    }
  }
  ierr = VecRestoreArray(X,&x);CHKERRQ(ierr);
  return 0;
}

PetscErrorCode StokesCalcError(Stokes *s)
{
  PetscScalar    scale = PetscSqrtReal((double)s->nx*s->ny);
  PetscReal      val;
  Vec            y0, y1;
  PetscErrorCode ierr;

  PetscFunctionBeginUser;
  /* error y-x */
  ierr = VecAXPY(s->y, -1.0, s->x);CHKERRQ(ierr);
  /* ierr = VecView(s->y, (PetscViewer)PETSC_VIEWER_DEFAULT);CHKERRQ(ierr); */

  /* error in velocity */
  ierr = VecGetSubVector(s->y, s->isg[0], &y0);CHKERRQ(ierr);
  ierr = VecNorm(y0, NORM_2, &val);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," discretization error u = %g\n",(double)(PetscRealPart(val/scale)));CHKERRQ(ierr);
  ierr = VecRestoreSubVector(s->y, s->isg[0], &y0);CHKERRQ(ierr);

  /* error in pressure */
  ierr = VecGetSubVector(s->y, s->isg[1], &y1);CHKERRQ(ierr);
  ierr = VecNorm(y1, NORM_2, &val);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," discretization error p = %g\n",(double)(PetscRealPart(val/scale)));CHKERRQ(ierr);
  ierr = VecRestoreSubVector(s->y, s->isg[1], &y1);CHKERRQ(ierr);

  /* total error */
  ierr = VecNorm(s->y, NORM_2, &val);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," discretization error [u,p] = %g\n", (double)PetscRealPart((val/scale)));CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@
   PetscDTGaussQuadrature - create Gauss quadrature

   Not Collective

   Input Arguments:
+  npoints - number of points
.  a - left end of interval (often-1)
-  b - right end of interval (often +1)

   Output Arguments:
+  x - quadrature points
-  w - quadrature weights

   Level: intermediate

   References:
   Golub and Welsch, Calculation of Quadrature Rules, Math. Comp. 23(106), 221--230, 1969.

.seealso: PetscDTLegendreEval()
@*/
PetscErrorCode PetscDTGaussQuadrature(PetscInt npoints,PetscReal a,PetscReal b,PetscReal *x,PetscReal *w)
{
  PetscErrorCode ierr;
  PetscInt       i;
  PetscReal      *work;
  PetscScalar    *Z;
  PetscBLASInt   N,LDZ,info;

  PetscFunctionBegin;
  ierr = PetscCitationsRegister(GaussCitation, &GaussCite);CHKERRQ(ierr);
  /* Set up the Golub-Welsch system */
  for (i=0; i<npoints; i++) {
    x[i] = 0;                   /* diagonal is 0 */
    if (i) w[i-1] = 0.5 / PetscSqrtReal(1 - 1./PetscSqr(2*i));
  }
  ierr = PetscMalloc2(npoints*npoints,&Z,PetscMax(1,2*npoints-2),&work);CHKERRQ(ierr);
  ierr = PetscBLASIntCast(npoints,&N);CHKERRQ(ierr);
  LDZ  = N;
  ierr = PetscFPTrapPush(PETSC_FP_TRAP_OFF);CHKERRQ(ierr);
  PetscStackCallBLAS("LAPACKsteqr",LAPACKsteqr_("I",&N,x,w,Z,&LDZ,work,&info));
  ierr = PetscFPTrapPop();CHKERRQ(ierr);
  if (info) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"xSTEQR error");

  for (i=0; i<(npoints+1)/2; i++) {
    PetscReal y = 0.5 * (-x[i] + x[npoints-i-1]); /* enforces symmetry */
    x[i]           = (a+b)/2 - y*(b-a)/2;
    x[npoints-i-1] = (a+b)/2 + y*(b-a)/2;

    w[i] = w[npoints-1-i] = 0.5*(b-a)*(PetscSqr(PetscAbsScalar(Z[i*npoints])) + PetscSqr(PetscAbsScalar(Z[(npoints-i-1)*npoints])));
  }
  ierr = PetscFree2(Z,work);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/* 
   FormInitialGuess - Forms initial approximation.

   Input Parameters:
   user - user-defined application context
   X - vector

   Output Parameter:
   X - vector
 */
PetscErrorCode FormInitialGuess(AppCtx *user,Vec X)
{
  PetscInt       i,j,row,mx,my,xs,ys,xm,ym,gxm,gym,gxs,gys;
  PetscErrorCode ierr;
  PetscReal      one = 1.0,lambda,temp1,temp,hx,hy,hxdhy,hydhx,sc;
  PetscScalar    *x;
  Vec            localX = user->localX;

  mx = user->mx;            my = user->my;            lambda = user->param;
  hx = one/(PetscReal)(mx-1);  hy = one/(PetscReal)(my-1);
  sc = hx*hy*lambda;        hxdhy = hx/hy;            hydhx = hy/hx;
  temp1 = lambda/(lambda + one);

  /*
     Get a pointer to vector data.
       - For default PETSc vectors,VecGetArray() returns a pointer to
         the data array.  Otherwise, the routine is implementation dependent.
       - You MUST call VecRestoreArray() when you no longer need access to
         the array.
  */
  ierr = VecGetArray(localX,&x);CHKERRQ(ierr);

  /*
     Get local grid boundaries (for 2-dimensional DMDA):
       xs, ys   - starting grid indices (no ghost points)
       xm, ym   - widths of local grid (no ghost points)
       gxs, gys - starting grid indices (including ghost points)
       gxm, gym - widths of local grid (including ghost points)
  */
  ierr = DMDAGetCorners(user->da,&xs,&ys,PETSC_NULL,&xm,&ym,PETSC_NULL);CHKERRQ(ierr);
  ierr = DMDAGetGhostCorners(user->da,&gxs,&gys,PETSC_NULL,&gxm,&gym,PETSC_NULL);CHKERRQ(ierr);

  /*
     Compute initial guess over the locally owned part of the grid
  */
  for (j=ys; j<ys+ym; j++) {
    temp = (PetscReal)(PetscMin(j,my-j-1))*hy;
    for (i=xs; i<xs+xm; i++) {
      row = i - gxs + (j - gys)*gxm; 
      if (i == 0 || j == 0 || i == mx-1 || j == my-1) {
        x[row] = 0.0; 
        continue;
      }
      x[row] = temp1*PetscSqrtReal(PetscMin((PetscReal)(PetscMin(i,mx-i-1))*hx,temp)); 
    }
  }

  /*
     Restore vector
  */
  ierr = VecRestoreArray(localX,&x);CHKERRQ(ierr);

  /*
     Insert values into global vector
  */
  ierr = DMLocalToGlobalBegin(user->da,localX,INSERT_VALUES,X);CHKERRQ(ierr);
  ierr = DMLocalToGlobalEnd(user->da,localX,INSERT_VALUES,X);CHKERRQ(ierr);
  return 0;
} 

/*
   Monitor - User-provided routine to monitor the solution computed at
   each timestep.  This example plots the solution and computes the
   error in two different norms.

   Input Parameters:
   ts     - the timestep context
   step   - the count of the current step (with 0 meaning the
             initial condition)
   time   - the current time
   u      - the solution at this timestep
   ctx    - the user-provided context for this monitoring routine.
            In this case we use the application context which contains
            information about the problem size, workspace and the exact
            solution.
*/
PetscErrorCode Monitor(TS ts,PetscInt step,PetscReal time,Vec u,void *ctx)
{
  AppCtx         *appctx = (AppCtx*) ctx;   /* user-defined application context */
  PetscErrorCode ierr;
  PetscReal      norm_2,norm_max;

  /*
     View a graph of the current iterate
  */
  ierr = VecView(u,appctx->viewer2);CHKERRQ(ierr);

  /*
     Compute the exact solution
  */
  ierr = ExactSolution(time,appctx->solution,appctx);CHKERRQ(ierr);

  /*
     Print debugging information if desired
  */
  if (appctx->debug) {
    ierr = PetscPrintf(appctx->comm,"Computed solution vector\n");CHKERRQ(ierr);
    ierr = VecView(u,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
    ierr = PetscPrintf(appctx->comm,"Exact solution vector\n");CHKERRQ(ierr);
    ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  }

  /*
     Compute the 2-norm and max-norm of the error
  */
  ierr   = VecAXPY(appctx->solution,-1.0,u);CHKERRQ(ierr);
  ierr   = VecNorm(appctx->solution,NORM_2,&norm_2);CHKERRQ(ierr);
  norm_2 = PetscSqrtReal(appctx->h)*norm_2;
  ierr   = VecNorm(appctx->solution,NORM_MAX,&norm_max);CHKERRQ(ierr);
  if (norm_2   < 1e-14) norm_2   = 0;
  if (norm_max < 1e-14) norm_max = 0;

  /*
     PetscPrintf() causes only the first processor in this
     communicator to print the timestep information.
  */
  ierr = PetscPrintf(appctx->comm,"Timestep %D: time = %g 2-norm error = %g max norm error = %g\n",step,(double)time,(double)norm_2,(double)norm_max);CHKERRQ(ierr);
  appctx->norm_2   += norm_2;
  appctx->norm_max += norm_max;

  /*
     View a graph of the error
  */
  ierr = VecView(appctx->solution,appctx->viewer1);CHKERRQ(ierr);

  /*
     Print debugging information if desired
  */
  if (appctx->debug) {
    ierr = PetscPrintf(appctx->comm,"Error vector\n");CHKERRQ(ierr);
    ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  }

  return 0;
}

/*@C
   PetscDrawViewPortsCreate - Splits a window into smaller view ports. Each processor shares all the viewports.

   Collective on PetscDraw

   Input Parameters:
+  draw - the drawing context
-  nports - the number of ports

   Output Parameter:
.  ports - a PetscDrawViewPorts context (C structure)

   Options Database:
.  -draw_ports - display multiple fields in the same window with PetscDrawPorts instead of in seperate windows

   Level: advanced

   Concepts: drawing^in subset of window

.seealso: PetscDrawSplitViewPort(), PetscDrawSetViewPort(), PetscDrawViewPortsSet(), PetscDrawViewPortsDestroy()

@*/
PetscErrorCode  PetscDrawViewPortsCreate(PetscDraw draw,PetscInt nports,PetscDrawViewPorts **newports)
{
  PetscDrawViewPorts *ports;
  PetscInt           i,n;
  PetscBool          isnull;
  PetscMPIInt        rank;
  PetscReal          *xl,*xr,*yl,*yr,h;
  PetscErrorCode     ierr;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(draw,PETSC_DRAW_CLASSID,1);
  if (nports < 1) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE, "Number of divisions must be positive: %d", nports);
  PetscValidPointer(newports,3);
  ierr = PetscDrawIsNull(draw,&isnull);CHKERRQ(ierr);
  if (isnull) {*newports = NULL; PetscFunctionReturn(0);}
  ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)draw),&rank);CHKERRQ(ierr);

  ierr = PetscNew(&ports);CHKERRQ(ierr); *newports = ports;
  ports->draw = draw;
  ports->nports = nports;
  ierr = PetscObjectReference((PetscObject)draw);CHKERRQ(ierr);
  /* save previous drawport of window */
  ierr = PetscDrawGetViewPort(draw,&ports->port_xl,&ports->port_yl,&ports->port_xr,&ports->port_yr);CHKERRQ(ierr);

  n = (PetscInt)(.1 + PetscSqrtReal((PetscReal)nports));
  while (n*n < nports) n++;
  h = 1.0/n;

  ierr = PetscMalloc4(n*n,&xl,n*n,&xr,n*n,&yl,n*n,&yr);CHKERRQ(ierr);
  ports->xl = xl;
  ports->xr = xr;
  ports->yl = yl;
  ports->yr = yr;

  ierr = PetscDrawSetCoordinates(draw,0.0,0.0,1.0,1.0);CHKERRQ(ierr);
  ierr = PetscDrawCollectiveBegin(draw);CHKERRQ(ierr);
  for (i=0; i<n*n; i++) {
    xl[i] = (i % n)*h;
    xr[i] = xl[i] + h;
    yl[i] = (i / n)*h;
    yr[i] = yl[i] + h;

    if (!rank) {
      ierr = PetscDrawLine(draw,xl[i],yl[i],xl[i],yr[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
      ierr = PetscDrawLine(draw,xl[i],yr[i],xr[i],yr[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
      ierr = PetscDrawLine(draw,xr[i],yr[i],xr[i],yl[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
      ierr = PetscDrawLine(draw,xr[i],yl[i],xl[i],yl[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
    }

    xl[i] += .05*h;
    xr[i] -= .05*h;
    yl[i] += .05*h;
    yr[i] -= .05*h;
  }
  ierr = PetscDrawCollectiveEnd(draw);CHKERRQ(ierr);
  ierr = PetscDrawFlush(draw);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*
   FormInitialGuess - Forms initial approximation.

   Input Parameters:
   user - user-defined application context
   X - vector

   Output Parameter:
   X - vector
 */
PetscErrorCode FormInitialGuess(AppCtx *user,Vec X)
{
  PetscInt       i,j,k,Mx,My,Mz,xs,ys,zs,xm,ym,zm;
  PetscErrorCode ierr;
  PetscReal      lambda,temp1,hx,hy,hz,tempk,tempj;
  PetscScalar    ***x;

  PetscFunctionBeginUser;
  ierr = DMDAGetInfo(user->da,PETSC_IGNORE,&Mx,&My,&Mz,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);CHKERRQ(ierr);

  lambda = user->param;
  hx     = 1.0/(PetscReal)(Mx-1);
  hy     = 1.0/(PetscReal)(My-1);
  hz     = 1.0/(PetscReal)(Mz-1);
  temp1  = lambda/(lambda + 1.0);

  /*
     Get a pointer to vector data.
       - For default PETSc vectors, VecGetArray() returns a pointer to
         the data array.  Otherwise, the routine is implementation dependent.
       - You MUST call VecRestoreArray() when you no longer need access to
         the array.
  */
  ierr = DMDAVecGetArray(user->da,X,&x);CHKERRQ(ierr);

  /*
     Get local grid boundaries (for 3-dimensional DMDA):
       xs, ys, zs   - starting grid indices (no ghost points)
       xm, ym, zm   - widths of local grid (no ghost points)

  */
  ierr = DMDAGetCorners(user->da,&xs,&ys,&zs,&xm,&ym,&zm);CHKERRQ(ierr);

  /*
     Compute initial guess over the locally owned part of the grid
  */
  for (k=zs; k<zs+zm; k++) {
    tempk = (PetscReal)(PetscMin(k,Mz-k-1))*hz;
    for (j=ys; j<ys+ym; j++) {
      tempj = PetscMin((PetscReal)(PetscMin(j,My-j-1))*hy,tempk);
      for (i=xs; i<xs+xm; i++) {
        if (i == 0 || j == 0 || k == 0 || i == Mx-1 || j == My-1 || k == Mz-1) {
          /* boundary conditions are all zero Dirichlet */
          x[k][j][i] = 0.0;
        } else {
          x[k][j][i] = temp1*PetscSqrtReal(PetscMin((PetscReal)(PetscMin(i,Mx-i-1))*hx,tempj));
        }
      }
    }
  }

  /*
     Restore vector
  */
  ierr = DMDAVecRestoreArray(user->da,X,&x);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*
   Monitor - User-provided routine to monitor the solution computed at
   each timestep.  This example plots the solution and computes the
   error in two different norms.

   Input Parameters:
   ts     - the timestep context
   step   - the count of the current step (with 0 meaning the
             initial condition)
   time   - the current time
   u      - the solution at this timestep
   ctx    - the user-provided context for this monitoring routine.
            In this case we use the application context which contains
            information about the problem size, workspace and the exact
            solution.
*/
PetscErrorCode Monitor(TS ts,PetscInt step,PetscReal time,Vec u,void *ctx)
{
  AppCtx         *appctx = (AppCtx*) ctx;   /* user-defined application context */
  PetscErrorCode ierr;
  PetscReal      norm_2,norm_max;

  /*
     View a graph of the current iterate
  */
  ierr = VecView(u,appctx->viewer2);CHKERRQ(ierr);

  /*
     Compute the exact solution
  */
  ierr = ExactSolution(time,appctx->solution,appctx);CHKERRQ(ierr);

  /*
     Print debugging information if desired
  */
  if (appctx->debug) {
     printf("Computed solution vector\n");
     ierr = VecView(u,PETSC_VIEWER_STDOUT_SELF);CHKERRQ(ierr);
     printf("Exact solution vector\n");
     ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_SELF);CHKERRQ(ierr);
  }

  /*
     Compute the 2-norm and max-norm of the error
  */
  ierr = VecAXPY(appctx->solution,-1.0,u);CHKERRQ(ierr);
  ierr = VecNorm(appctx->solution,NORM_2,&norm_2);CHKERRQ(ierr);
  norm_2 = PetscSqrtReal(appctx->h)*norm_2;
  ierr = VecNorm(appctx->solution,NORM_MAX,&norm_max);CHKERRQ(ierr);

  ierr = PetscPrintf(PETSC_COMM_WORLD,"Timestep %D: time = %G, 2-norm error = %G, max norm error = %G\n",
         step,time,norm_2,norm_max);CHKERRQ(ierr);
  appctx->norm_2   += norm_2;
  appctx->norm_max += norm_max;

  /*
     View a graph of the error
  */
  ierr = VecView(appctx->solution,appctx->viewer1);CHKERRQ(ierr);

  /*
     Print debugging information if desired
  */
  if (appctx->debug) {
     printf("Error vector\n");
     ierr = VecView(appctx->solution,PETSC_VIEWER_STDOUT_SELF);CHKERRQ(ierr);
  }

  return 0;
}

PetscErrorCode KSPAGMRESLejaOrdering(PetscScalar *re, PetscScalar *im, PetscScalar *rre, PetscScalar *rim, PetscInt m)
{
  PetscInt       *spos;
  PetscScalar    *n_cmpl,temp;
  PetscErrorCode  ierr;
  PetscInt        i, pos, j;
  ierr = PetscMalloc(m*sizeof(PetscScalar), &n_cmpl);CHKERRQ(ierr);
  ierr = PetscMalloc(m*sizeof(PetscInt), &spos);CHKERRQ(ierr);

  PetscFunctionBegin;
  /* Check the proper order of complex conjugate pairs */
  j = 0;
  while (j  < m ) {
    if (im[j] != 0.0) {/* complex eigenvalue */
      if (im[j] < 0.0) { /* change the order */
        temp = im[j+1];
        im[j+1] = im[j];
        im[j] = temp;
      }
      j += 2;
    } else j++;
  }

  for (i = 0;i < m;i++)
    n_cmpl[i] = PetscSqrtReal(re[i]*re[i]+im[i]*im[i]);
  KSPAGMRESLejafmaxarray(n_cmpl, 0, m, &pos);
  j = 0;
  if (im[pos] >= 0.0) {
    rre[0] = re[pos];
    rim[0] = im[pos];
    j++;
    spos[0] = pos;
  }
  while (j < (m)) {
    if (im[pos] > 0) {
      rre[j] = re[pos+1];
      rim[j] = im[pos+1];
      spos[j] = pos + 1;
      j++;
    }
    KSPAGMRESLejaCfpdMax(re, im, spos, j, m, &pos);
    if (im[pos] < 0) pos--;

    if ((im[pos] >= 0) && (j < m)) {
      rre[j] = re[pos];
      rim[j] = im[pos];
      spos[j] = pos;
      j++;
    }
  }
  ierr = PetscFree(spos);CHKERRQ(ierr);
  ierr = PetscFree(n_cmpl);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@C
   PetscDrawViewPortsCreate - Splits a window into smaller
       view ports. Each processor shares all the viewports.

   Collective on PetscDraw

   Input Parameters:
+  draw - the drawing context
-  nports - the number of ports

   Output Parameter:
.  ports - a PetscDrawViewPorts context (C structure)

   Level: advanced

   Concepts: drawing^in subset of window

.seealso: PetscDrawSplitViewPort(), PetscDrawSetViewPort(), PetscDrawViewPortsSet(), PetscDrawViewPortsDestroy()

@*/
PetscErrorCode  PetscDrawViewPortsCreate(PetscDraw draw,PetscInt nports,PetscDrawViewPorts **ports)
{
  PetscInt       i,n;
  PetscErrorCode ierr;
  PetscBool      isnull;
  PetscReal      *xl,*xr,*yl,*yr,h;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(draw,PETSC_DRAW_CLASSID,1);
  PetscValidPointer(ports,3);
  ierr = PetscObjectTypeCompare((PetscObject)draw,PETSC_DRAW_NULL,&isnull);CHKERRQ(ierr);
  if (isnull) {
    *ports = NULL;
    PetscFunctionReturn(0);
  }

  ierr             = PetscNew(ports);CHKERRQ(ierr);
  (*ports)->draw   = draw;
  (*ports)->nports = nports;

  ierr = PetscObjectReference((PetscObject)draw);CHKERRQ(ierr);

  n = (PetscInt)(.1 + PetscSqrtReal((PetscReal)nports));
  while (n*n < nports) n++;

  ierr = PetscMalloc1(n*n,&xl);CHKERRQ(ierr);(*ports)->xl = xl;
  ierr = PetscMalloc1(n*n,&xr);CHKERRQ(ierr);(*ports)->xr = xr;
  ierr = PetscMalloc1(n*n,&yl);CHKERRQ(ierr);(*ports)->yl = yl;
  ierr = PetscMalloc1(n*n,&yr);CHKERRQ(ierr);(*ports)->yr = yr;

  h = 1.0/n;

  for (i=0; i<n*n; i++) {
    xl[i] = (i % n)*h;
    xr[i] = xl[i] + h;
    yl[i] = (i/n)*h;
    yr[i] = yl[i] + h;

    ierr = PetscDrawLine(draw,xl[i],yl[i],xl[i],yr[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
    ierr = PetscDrawLine(draw,xl[i],yr[i],xr[i],yr[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
    ierr = PetscDrawLine(draw,xr[i],yr[i],xr[i],yl[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);
    ierr = PetscDrawLine(draw,xr[i],yl[i],xl[i],yl[i],PETSC_DRAW_BLACK);CHKERRQ(ierr);

    xl[i] += .1*h;
    xr[i] -= .1*h;
    yl[i] += .1*h;
    yr[i] -= .1*h;
  }
  /* save previous drawport of window */
  ierr = PetscDrawGetViewPort(draw,&(*ports)->port_xl,&(*ports)->port_yl,&(*ports)->port_xr,&(*ports)->port_yr);CHKERRQ(ierr);
  /* ierr = PetscDrawSynchronizedFlush(draw);CHKERRQ(ierr);*/  /* this causes flicker */
  PetscFunctionReturn(0);
}

/*
  Custom CGS orthogonalization, preprocess after first orthogonalization
*/
static PetscErrorCode SVDOrthogonalizeCGS(BV V,PetscInt i,PetscScalar* h,PetscReal a,BVOrthogRefineType refine,PetscReal eta,PetscReal *norm)
{
  PetscErrorCode ierr;
  PetscReal      sum,onorm;
  PetscScalar    dot;
  PetscInt       j;

  PetscFunctionBegin;
  switch (refine) {
  case BV_ORTHOG_REFINE_NEVER:
    ierr = BVNormColumn(V,i,NORM_2,norm);CHKERRQ(ierr);
    break;
  case BV_ORTHOG_REFINE_ALWAYS:
    ierr = BVSetActiveColumns(V,0,i);CHKERRQ(ierr);
    ierr = BVDotColumn(V,i,h);CHKERRQ(ierr);
    ierr = BVMultColumn(V,-1.0,1.0,i,h);CHKERRQ(ierr);
    ierr = BVNormColumn(V,i,NORM_2,norm);CHKERRQ(ierr);
    break;
  case BV_ORTHOG_REFINE_IFNEEDED:
    dot = h[i];
    onorm = PetscSqrtReal(PetscRealPart(dot)) / a;
    sum = 0.0;
    for (j=0;j<i;j++) {
      sum += PetscRealPart(h[j] * PetscConj(h[j]));
    }
    *norm = PetscRealPart(dot)/(a*a) - sum;
    if (*norm>0.0) *norm = PetscSqrtReal(*norm);
    else {
      ierr = BVNormColumn(V,i,NORM_2,norm);CHKERRQ(ierr);
    }
    if (*norm < eta*onorm) {
      ierr = BVSetActiveColumns(V,0,i);CHKERRQ(ierr);
      ierr = BVDotColumn(V,i,h);CHKERRQ(ierr);
      ierr = BVMultColumn(V,-1.0,1.0,i,h);CHKERRQ(ierr);
      ierr = BVNormColumn(V,i,NORM_2,norm);CHKERRQ(ierr);
    }
    break;
  }
  PetscFunctionReturn(0);
}

/*@C
   DMDAGetLogicalCoordinate - Returns a the i,j,k logical coordinate for the closest mesh point to a x,y,z point in the coordinates of the DMDA

   Collective on DMDA

   Input Parameters:
+  da - the distributed array
-  x,y,z - the physical coordinates

   Output Parameters:
+   II, JJ, KK - the logical coordinate (-1 on processes that do not contain that point)
-   X, Y, Z, - (optional) the coordinates of the located grid point

   Level: advanced

   Notes:
   All processors that share the DMDA must call this with the same coordinate value

.keywords: distributed array, get, processor subset
@*/
PetscErrorCode  DMDAGetLogicalCoordinate(DM da,PetscScalar x,PetscScalar y,PetscScalar z,PetscInt *II,PetscInt *JJ,PetscInt *KK,PetscScalar *X,PetscScalar *Y,PetscScalar *Z)
{
  DM_DA          *dd = (DM_DA*)da->data;
  PetscErrorCode ierr;
  Vec            coors;
  DM             dacoors;
  DMDACoor2d     **c;
  PetscInt       i,j,xs,xm,ys,ym;
  PetscReal      d,D = PETSC_MAX_REAL,Dv;
  PetscMPIInt    rank,root;

  PetscFunctionBegin;
  if (dd->dim == 1) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Cannot get point from 1d DMDA");
  if (dd->dim == 3) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Cannot get point from 3d DMDA");

  *II = -1;
  *JJ = -1;

  ierr = DMGetCoordinateDM(da,&dacoors);CHKERRQ(ierr);
  ierr = DMDAGetCorners(dacoors,&xs,&ys,NULL,&xm,&ym,NULL);CHKERRQ(ierr);
  ierr = DMGetCoordinates(da,&coors);CHKERRQ(ierr);
  ierr = DMDAVecGetArray(dacoors,coors,&c);CHKERRQ(ierr);
  for (j=ys; j<ys+ym; j++) {
    for (i=xs; i<xs+xm; i++) {
      d = PetscSqrtReal(PetscRealPart( (c[j][i].x - x)*(c[j][i].x - x) + (c[j][i].y - y)*(c[j][i].y - y) ));
      if (d < D) {
        D   = d;
        *II = i;
        *JJ = j;
      }
    }
  }
  ierr = MPI_Allreduce(&D,&Dv,1,MPIU_REAL,MPI_MIN,PetscObjectComm((PetscObject)da));CHKERRQ(ierr);
  if (D != Dv) {
    *II  = -1;
    *JJ  = -1;
    rank = 0;
  } else {
    *X = c[*JJ][*II].x;
    *Y = c[*JJ][*II].y;
    ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)da),&rank);CHKERRQ(ierr);
    rank++;
  }
  ierr = MPI_Allreduce(&rank,&root,1,MPI_INT,MPI_SUM,PetscObjectComm((PetscObject)da));CHKERRQ(ierr);
  root--;
  ierr = MPI_Bcast(X,1,MPIU_SCALAR,root,PetscObjectComm((PetscObject)da));CHKERRQ(ierr);
  ierr = MPI_Bcast(Y,1,MPIU_SCALAR,root,PetscObjectComm((PetscObject)da));CHKERRQ(ierr);
  ierr = DMDAVecRestoreArray(dacoors,coors,&c);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PetscErrorCode SNESNGMRESSelectRestart_Private(SNES snes,PetscInt l,PetscReal fAnorm,PetscReal dnorm,PetscReal fminnorm,PetscReal dminnorm,PetscBool *selectRestart)
{
  SNES_NGMRES    *ngmres = (SNES_NGMRES*)snes->data;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  *selectRestart = PETSC_FALSE;
  /* difference stagnation restart */
  if ((ngmres->epsilonB*dnorm > dminnorm) && (PetscSqrtReal(fAnorm) > ngmres->deltaB*PetscSqrtReal(fminnorm)) && l > 0) {
    if (ngmres->monitor) {
      ierr = PetscViewerASCIIPrintf(ngmres->monitor,"difference restart: %e > %e\n",ngmres->epsilonB*dnorm,dminnorm);CHKERRQ(ierr);
    }
    *selectRestart = PETSC_TRUE;
  }
  /* residual stagnation restart */
  if (PetscSqrtReal(fAnorm) > ngmres->gammaC*PetscSqrtReal(fminnorm)) {
    if (ngmres->monitor) {
      ierr = PetscViewerASCIIPrintf(ngmres->monitor,"residual restart: %e > %e\n",PetscSqrtReal(fAnorm),ngmres->gammaC*PetscSqrtReal(fminnorm));CHKERRQ(ierr);
    }
    *selectRestart = PETSC_TRUE;
  }
  PetscFunctionReturn(0);
}

PetscErrorCode VecNorm_MPI(Vec xin,NormType type,PetscReal *z)
{
  PetscReal         sum,work = 0.0;
  const PetscScalar *xx;
  PetscErrorCode    ierr;
  PetscInt          n   = xin->map->n;
  PetscBLASInt      one = 1,bn;

  PetscFunctionBegin;
  ierr = PetscBLASIntCast(n,&bn);CHKERRQ(ierr);
  if (type == NORM_2 || type == NORM_FROBENIUS) {
    ierr = VecGetArrayRead(xin,&xx);CHKERRQ(ierr);
    work = PetscRealPart(BLASdot_(&bn,xx,&one,xx,&one));
    ierr = VecRestoreArrayRead(xin,&xx);CHKERRQ(ierr);
    ierr = MPIU_Allreduce(&work,&sum,1,MPIU_REAL,MPIU_SUM,PetscObjectComm((PetscObject)xin));CHKERRQ(ierr);
    *z   = PetscSqrtReal(sum);
    ierr = PetscLogFlops(2.0*xin->map->n);CHKERRQ(ierr);
  } else if (type == NORM_1) {
    /* Find the local part */
    ierr = VecNorm_Seq(xin,NORM_1,&work);CHKERRQ(ierr);
    /* Find the global max */
    ierr = MPIU_Allreduce(&work,z,1,MPIU_REAL,MPIU_SUM,PetscObjectComm((PetscObject)xin));CHKERRQ(ierr);
  } else if (type == NORM_INFINITY) {
    /* Find the local max */
    ierr = VecNorm_Seq(xin,NORM_INFINITY,&work);CHKERRQ(ierr);
    /* Find the global max */
    ierr = MPIU_Allreduce(&work,z,1,MPIU_REAL,MPIU_MAX,PetscObjectComm((PetscObject)xin));CHKERRQ(ierr);
  } else if (type == NORM_1_AND_2) {
    PetscReal temp[2];
    ierr = VecNorm_Seq(xin,NORM_1,temp);CHKERRQ(ierr);
    ierr = VecNorm_Seq(xin,NORM_2,temp+1);CHKERRQ(ierr);
    temp[1] = temp[1]*temp[1];
    ierr = MPIU_Allreduce(temp,z,2,MPIU_REAL,MPIU_SUM,PetscObjectComm((PetscObject)xin));CHKERRQ(ierr);
    z[1] = PetscSqrtReal(z[1]);
  }
  PetscFunctionReturn(0);
}