/*$Id: snesj2.c,v 1.24 2000/05/05 22:18:12 balay Exp balay $*/

#include "src/mat/matimpl.h"      /*I  "petscmat.h"  I*/
#include "src/snes/snesimpl.h"    /*I  "petscsnes.h"  I*/

#undef __FUNC__  
#define __FUNC__ /*<a name=""></a>*/"SNESDefaultComputeJacobianColor"
/*@C
    SNESDefaultComputeJacobianColor - Computes the Jacobian using
    finite differences and coloring to exploit matrix sparsity. 
  
    Collective on SNES

    Input Parameters:
+   snes - nonlinear solver object
.   x1 - location at which to evaluate Jacobian
-   ctx - coloring context, where ctx must have type MatFDColoring, 
          as created via MatFDColoringCreate()

    Output Parameters:
+   J - Jacobian matrix (not altered in this routine)
.   B - newly computed Jacobian matrix to use with preconditioner (generally the same as J)
-   flag - flag indicating whether the matrix sparsity structure has changed

    Options Database Keys:
.  -mat_fd_coloring_freq <freq> - Activates SNESDefaultComputeJacobianColor()

    Level: intermediate

.keywords: SNES, finite differences, Jacobian, coloring, sparse

.seealso: SNESSetJacobian(), SNESTestJacobian(), SNESDefaultComputeJacobian()
          TSDefaultComputeJacobianColor(), MatFDColoringCreate(),
          MatFDColoringSetFunction()

@*/
int SNESDefaultComputeJacobianColor(SNES snes,Vec x1,Mat *J,Mat *B,MatStructure *flag,void *ctx)
{
  MatFDColoring color = (MatFDColoring) ctx;
  int           ierr,freq,it;

  PetscFunctionBegin;
  ierr = MatFDColoringGetFrequency(color,&freq);CHKERRQ(ierr);
  ierr = SNESGetIterationNumber(snes,&it);CHKERRQ(ierr);

  if ((freq > 1) && ((it % freq) != 1)) {
    PLogInfo(color,"SNESDefaultComputeJacobianColor:Skipping Jacobian, it %d, freq %d\n",it,freq);
    *flag = SAME_PRECONDITIONER;
    PetscFunctionReturn(0);
  } else {
    PLogInfo(color,"SNESDefaultComputeJacobianColor:Computing Jacobian, it %d, freq %d\n",it,freq);
    *flag = SAME_NONZERO_PATTERN;
  }


  ierr = PLogEventBegin(SNES_FunctionEval,snes,x1,0,0);CHKERRQ(ierr);
  PetscStackPush("SNES user function");
  ierr = MatFDColoringApply(*B,color,x1,flag,snes);CHKERRQ(ierr);
  PetscStackPop;
  snes->nfuncs++;
  ierr = PLogEventEnd(SNES_FunctionEval,snes,x1,0,0);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}