Date: 2015-10-02T22:23:43+00:00

Actual source code: snesmfj.c
petsc-3.6.2 2015-10-02
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      2: #include <petsc/private/snesimpl.h>  /*I  "petscsnes.h" I*/
      3: #include <petscdm.h>                 /*I  "petscdm.h"   I*/
      4: #include <../src/mat/impls/mffd/mffdimpl.h>
      5: #include <petsc/private/matimpl.h>

      9: /*@C
     10:    MatMFFDComputeJacobian - Tells the matrix-free Jacobian object the new location at which
     11:        Jacobian matrix vector products will be computed at, i.e. J(x) * a. The x is obtained
     12:        from the SNES object (using SNESGetSolution()).

     14:    Logically Collective on SNES

     16:    Input Parameters:
     17: +   snes - the nonlinear solver context
     18: .   x - the point at which the Jacobian vector products will be performed
     19: .   jac - the matrix-free Jacobian object
     20: .   B - either the same as jac or another matrix type (ignored)
     21: .   flag - not relevent for matrix-free form
     22: -   dummy - the user context (ignored)

     24:    Level: developer

     26:    Warning:
     27:       If MatMFFDSetBase() is ever called on jac then this routine will NO longer get
     28:     the x from the SNES object and MatMFFDSetBase() must from that point on be used to
     29:     change the base vector x.

     31:    Notes:
     32:      This can be passed into SNESSetJacobian() as the Jacobian evaluation function argument
     33:      when using a completely matrix-free solver,
     34:      that is the B matrix is also the same matrix operator. This is used when you select
     35:      -snes_mf but rarely used directly by users. (All this routine does is call MatAssemblyBegin/End() on
     36:      the Mat jac.)

     38: .seealso: MatMFFDGetH(), MatCreateSNESMF(), MatCreateMFFD(), MATMFFD,
     39:           MatMFFDSetHHistory(), MatMFFDSetFunctionError(), MatCreateMFFD(), SNESSetJacobian()

     41: @*/
     42: PetscErrorCode  MatMFFDComputeJacobian(SNES snes,Vec x,Mat jac,Mat B,void *dummy)
     43: {

     47:   MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
     48:   MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);
     49:   return(0);
     50: }

     52: PETSC_EXTERN PetscErrorCode MatAssemblyEnd_MFFD(Mat,MatAssemblyType);
     53: PETSC_EXTERN PetscErrorCode MatMFFDSetBase_MFFD(Mat,Vec,Vec);

     57: /*
     58:    MatAssemblyEnd_SNESMF - Calls MatAssemblyEnd_MFFD() and then sets the
     59:     base from the SNES context

     61: */
     62: PetscErrorCode MatAssemblyEnd_SNESMF(Mat J,MatAssemblyType mt)
     63: {
     65:   MatMFFD        j    = (MatMFFD)J->data;
     66:   SNES           snes = (SNES)j->ctx;
     67:   Vec            u,f;

     70:   MatAssemblyEnd_MFFD(J,mt);

     72:   SNESGetSolution(snes,&u);
     73:   if (j->func == (PetscErrorCode (*)(void*,Vec,Vec))SNESComputeFunction) {
     74:     SNESGetFunction(snes,&f,NULL,NULL);
     75:     MatMFFDSetBase_MFFD(J,u,f);
     76:   } else {
     77:     /* f value known by SNES is not correct for other differencing function */
     78:     MatMFFDSetBase_MFFD(J,u,NULL);
     79:   }
     80:   return(0);
     81: }

     83: /*
     84:     This routine resets the MatAssemblyEnd() for the MatMFFD created from MatCreateSNESMF() so that it NO longer
     85:   uses the solution in the SNES object to update the base. See the warning in MatCreateSNESMF().
     86: */
     89: PetscErrorCode  MatMFFDSetBase_SNESMF(Mat J,Vec U,Vec F)
     90: {

     94:   MatMFFDSetBase_MFFD(J,U,F);

     96:   J->ops->assemblyend = MatAssemblyEnd_MFFD;
     97:   return(0);
     98: }

    102: /*@
    103:    MatCreateSNESMF - Creates a matrix-free matrix context for use with
    104:    a SNES solver.  This matrix can be used as the Jacobian argument for
    105:    the routine SNESSetJacobian(). See MatCreateMFFD() for details on how
    106:    the finite difference computation is done.

    108:    Collective on SNES and Vec

    110:    Input Parameters:
    111: .  snes - the SNES context

    113:    Output Parameter:
    114: .  J - the matrix-free matrix

    116:    Level: advanced

    119:    Notes:
    120:      You can call SNESSetJacobian() with MatMFFDComputeJacobian() if you are using matrix and not a different
    121:      preconditioner matrix

    123:      If you wish to provide a different function to do differencing on to compute the matrix-free operator than
    124:      that provided to SNESSetFunction() then call MatMFFDSetFunction() with your function after this call.

    126:      The difference between this routine and MatCreateMFFD() is that this matrix
    127:      automatically gets the current base vector from the SNES object and not from an
    128:      explicit call to MatMFFDSetBase().

    130:    Warning:
    131:      If MatMFFDSetBase() is ever called on jac then this routine will NO longer get
    132:      the x from the SNES object and MatMFFDSetBase() must from that point on be used to
    133:      change the base vector x.

    135:    Warning:
    136:      Using a different function for the differencing will not work if you are using non-linear left preconditioning.

    139: .seealso: MatDestroy(), MatMFFDSetFunction(), MatMFFDSetFunctionError(), MatMFFDDSSetUmin()
    140:           MatMFFDSetHHistory(), MatMFFDResetHHistory(), MatCreateMFFD(),
    141:           MatMFFDGetH(), MatMFFDRegister(), MatMFFDComputeJacobian()

    143: @*/
    144: PetscErrorCode  MatCreateSNESMF(SNES snes,Mat *J)
    145: {
    147:   PetscInt       n,N;
    148:   MatMFFD        mf;

    151:   if (snes->vec_func) {
    152:     VecGetLocalSize(snes->vec_func,&n);
    153:     VecGetSize(snes->vec_func,&N);
    154:   } else if (snes->dm) {
    155:     Vec tmp;
    156:     DMGetGlobalVector(snes->dm,&tmp);
    157:     VecGetLocalSize(tmp,&n);
    158:     VecGetSize(tmp,&N);
    159:     DMRestoreGlobalVector(snes->dm,&tmp);
    160:   } else SETERRQ(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE,"Must call SNESSetFunction() or SNESSetDM() first");
    161:   MatCreateMFFD(PetscObjectComm((PetscObject)snes),n,n,N,N,J);
    162:   mf      = (MatMFFD)(*J)->data;
    163:   mf->ctx = snes;

    165:   if (snes->pc && snes->pcside == PC_LEFT) {
    166:     MatMFFDSetFunction(*J,(PetscErrorCode (*)(void*,Vec,Vec))SNESComputeFunctionDefaultNPC,snes);
    167:   } else {
    168:     MatMFFDSetFunction(*J,(PetscErrorCode (*)(void*,Vec,Vec))SNESComputeFunction,snes);
    169:   }

    171:   (*J)->ops->assemblyend = MatAssemblyEnd_SNESMF;

    173:   PetscObjectComposeFunction((PetscObject)*J,"MatMFFDSetBase_C",MatMFFDSetBase_SNESMF);
    174:   return(0);
    175: }