Actual source code: matnull.c

  1: #define PETSCMAT_DLL

  3: /*
  4:     Routines to project vectors out of null spaces.
  5: */

 7:  #include src/mat/matimpl.h
 8:  #include petscsys.h

 10: PetscCookie PETSCMAT_DLLEXPORT MAT_NULLSPACE_COOKIE = 0;

 14: /*@C
 15:    MatNullSpaceSetFunction - set a function that removes a null space from a vector
 16:    out of null spaces.

 18:    Collective on MatNullSpace

 20:    Input Parameters:
 21: +  sp - the null space object
 22: -  remove - the function that removes the null space

 24: .keywords: PC, null space, create

 26: .seealso: MatNullSpaceDestroy(), MatNullSpaceRemove(), KSPSetNullSpace(), MatNullSpace, MatNullSpaceCreate()
 27: @*/
 28: PetscErrorCode PETSCMAT_DLLEXPORT MatNullSpaceSetFunction(MatNullSpace sp, PetscErrorCode (*remove)(Vec,void*),void *ctx)
 29: {
 31:   sp->remove = remove;
 32:   sp->rmctx  = ctx;
 33:   return(0);
 34: }

 38: /*@C
 39:    MatNullSpaceCreate - Creates a data structure used to project vectors 
 40:    out of null spaces.

 42:    Collective on MPI_Comm

 44:    Input Parameters:
 45: +  comm - the MPI communicator associated with the object
 46: .  has_cnst - PETSC_TRUE if the null space contains the constant vector; otherwise PETSC_FALSE
 47: .  n - number of vectors (excluding constant vector) in null space
 48: -  vecs - the vectors that span the null space (excluding the constant vector);
 49:           these vectors must be orthonormal. These vectors are NOT copied, so do not change them
 50:           after this call. You should free the array that you pass in.

 52:    Output Parameter:
 53: .  SP - the null space context

 55:    Level: advanced

 57:   Users manual sections:
 58: .   Section 4.15 Solving Singular Systems

 60: .keywords: PC, null space, create

 62: .seealso: MatNullSpaceDestroy(), MatNullSpaceRemove(), KSPSetNullSpace(), MatNullSpace, MatNullSpaceSetFunction()
 63: @*/
 64: PetscErrorCode PETSCMAT_DLLEXPORT MatNullSpaceCreate(MPI_Comm comm,PetscTruth has_cnst,PetscInt n,const Vec vecs[],MatNullSpace *SP)
 65: {
 66:   MatNullSpace   sp;
 68:   PetscInt       i;

 71:   PetscHeaderCreate(sp,_p_MatNullSpace,int,MAT_NULLSPACE_COOKIE,0,"MatNullSpace",comm,MatNullSpaceDestroy,0);
 72:   PetscLogObjectMemory(sp,sizeof(struct _p_MatNullSpace));

 74:   sp->has_cnst = has_cnst;
 75:   sp->n        = n;
 76:   sp->vec      = PETSC_NULL;
 77:   if (n) {
 78:     PetscMalloc(n*sizeof(Vec),&sp->vecs);
 79:     for (i=0; i<n; i++) sp->vecs[i] = vecs[i];
 80:   } else {
 81:     sp->vecs = 0;
 82:   }

 84:   for (i=0; i<n; i++) {
 85:     PetscObjectReference((PetscObject)sp->vecs[i]);
 86:   }
 87:   *SP          = sp;
 88:   return(0);
 89: }

 93: /*@
 94:    MatNullSpaceDestroy - Destroys a data structure used to project vectors 
 95:    out of null spaces.

 97:    Collective on MatNullSpace

 99:    Input Parameter:
100: .  sp - the null space context to be destroyed

102:    Level: advanced

104: .keywords: PC, null space, destroy

106: .seealso: MatNullSpaceCreate(), MatNullSpaceRemove(), MatNullSpaceSetFunction()
107: @*/
108: PetscErrorCode PETSCMAT_DLLEXPORT MatNullSpaceDestroy(MatNullSpace sp)
109: {

113:   if (--sp->refct > 0) return(0);

115:   if (sp->vec) {VecDestroy(sp->vec);}
116:   if (sp->vecs) {
117:     VecDestroyVecs(sp->vecs,sp->n);
118:   }
119:   PetscHeaderDestroy(sp);
120:   return(0);
121: }

125: /*@
126:    MatNullSpaceRemove - Removes all the components of a null space from a vector.

128:    Collective on MatNullSpace

130:    Input Parameters:
131: +  sp - the null space context
132: .  vec - the vector from which the null space is to be removed 
133: -  out - if this is requested (not PETSC_NULL) then this is a vector with the null space removed otherwise
134:          the removal is done in-place (in vec)



138:    Level: advanced

140: .keywords: PC, null space, remove

142: .seealso: MatNullSpaceCreate(), MatNullSpaceDestroy(), MatNullSpaceSetFunction()
143: @*/
144: PetscErrorCode PETSCMAT_DLLEXPORT MatNullSpaceRemove(MatNullSpace sp,Vec vec,Vec *out)
145: {
146:   PetscScalar    sum;
148:   PetscInt       j,n = sp->n,N;
149:   Vec            l = vec;

152:   if (out) {
153:     if (!sp->vec) {
154:       VecDuplicate(vec,&sp->vec);
155:     }
156:     *out = sp->vec;
157:     VecCopy(vec,*out);
158:     l    = *out;
159:   }

161:   if (sp->has_cnst) {
162:     VecSum(l,&sum);
163:     VecGetSize(l,&N);
164:     sum  = sum/(-1.0*N);
165:     VecShift(l,sum);
166:   }

168:   for (j=0; j<n; j++) {
169:     VecDot(l,sp->vecs[j],&sum);
170:     sum  = -sum;
171:     VecAXPY(l,sum,sp->vecs[j]);
172:   }

174:   if (sp->remove){
175:     (*sp->remove)(l,sp->rmctx);
176:   }
177:   return(0);
178: }

182: /*@
183:    MatNullSpaceTest  - Tests if the claimed null space is really a
184:      null space of a matrix

186:    Collective on MatNullSpace

188:    Input Parameters:
189: +  sp - the null space context
190: -  mat - the matrix

192:    Level: advanced

194: .keywords: PC, null space, remove

196: .seealso: MatNullSpaceCreate(), MatNullSpaceDestroy(), MatNullSpaceSetFunction()
197: @*/
198: PetscErrorCode PETSCMAT_DLLEXPORT MatNullSpaceTest(MatNullSpace sp,Mat mat)
199: {
200:   PetscScalar    sum;
201:   PetscReal      nrm;
202:   PetscInt       j,n = sp->n,N,m;
204:   Vec            l,r;
205:   MPI_Comm       comm = sp->comm;
206:   PetscTruth     flg1,flg2;

209:   PetscOptionsHasName(PETSC_NULL,"-mat_null_space_test_view",&flg1);
210:   PetscOptionsHasName(PETSC_NULL,"-mat_null_space_test_view_draw",&flg2);

212:   if (!sp->vec) {
213:     if (n) {
214:       VecDuplicate(sp->vecs[0],&sp->vec);
215:     } else {
216:       MatGetLocalSize(mat,&m,PETSC_NULL);
217:       VecCreateMPI(sp->comm,m,PETSC_DETERMINE,&sp->vec);
218:     }
219:   }
220:   l    = sp->vec;

222:   if (sp->has_cnst) {
223:     VecDuplicate(l,&r);
224:     VecGetSize(l,&N);
225:     sum  = 1.0/N;
226:     VecSet(l,sum);
227:     MatMult(mat,l,r);
228:     VecNorm(r,NORM_2,&nrm);
229:     if (nrm < 1.e-7) {PetscPrintf(comm,"Constants are likely null vector");}
230:     else {PetscPrintf(comm,"Constants are unlikely null vector ");}
231:     PetscPrintf(comm,"|| A * 1 || = %g\n",nrm);
232:     if (nrm > 1.e-7 && flg1) {VecView(r,PETSC_VIEWER_STDOUT_(comm));}
233:     if (nrm > 1.e-7 && flg2) {VecView(r,PETSC_VIEWER_DRAW_(comm));}
234:     VecDestroy(r);
235:   }

237:   for (j=0; j<n; j++) {
238:     (*mat->ops->mult)(mat,sp->vecs[j],l);
239:     VecNorm(l,NORM_2,&nrm);
240:     if (nrm < 1.e-7) {PetscPrintf(comm,"Null vector %D is likely null vector",j);}
241:     else {PetscPrintf(comm,"Null vector %D unlikely null vector ",j);}
242:     PetscPrintf(comm,"|| A * v[%D] || = %g\n",j,nrm);
243:     if (nrm > 1.e-7 && flg1) {VecView(l,PETSC_VIEWER_STDOUT_(comm));}
244:     if (nrm > 1.e-7 && flg2) {VecView(l,PETSC_VIEWER_DRAW_(comm));}
245:   }

247:   if (sp->remove){
248:     SETERRQ(PETSC_ERR_SUP,"Cannot test a null space provided as a function with MatNullSpaceSetFunction()");
249:   }
250: 
251:   return(0);
252: }