initial values of matrix and vector

[Yixun Liu]

You mean I have no need to call
VecSet(v, 0.0); and
MatZeroEntries(mat);

after I set the size for the vector or matrix?






Barry Smith wrote:
>
> Jed is right. Our intention is to have the vector initialized to zero
> at creation time IF we allocate the array space.
> Tracking down a not properly initialized vector is the type of bug
> that takes forever to find; plus I wanted consistency
> between vectors and matrix. Users SHOULD NOT call a MatZeroEntries()
> initially on matrices (since it screws up
> preallocation) so we should not have them do it on vectors either for
> consistency.
>
> Barry
>
> On Feb 24, 2009, at 10:57 AM, Jed Brown wrote:
>
>> On Tue 2009-02-24 06:53, Matthew Knepley wrote:
>>> On Mon, Feb 23, 2009 at 8:26 PM, Barry Smith <bsmith at mcs.anl.gov>
>>> wrote:
>>>
>>>
>>> Vectors have all entries equal to zero. Dense matrices have all entries
>>> equal to zero. Sparse matrices have no entries (logically this is
>>> the same
>>> as entries equal to zero).
>>>
>>>
>>> We do not automatically zero the entires upon allocation. You have
>>> to call
>>> VecZeroEntries() or VecSet()
>>> to initialize the vector.
>>
>> That's what I would have expected, but Barry is correct, at least for
>> the usual types. See, for instance
>>
>> PetscErrorCode PETSCVEC_DLLEXPORT VecCreate_Seq(Vec V)
>> {
>> Vec_Seq *s;
>> PetscScalar *array;
>> PetscErrorCode ierr;
>> PetscInt n = PetscMax(V->map->n,V->map->N);
>> PetscMPIInt size;
>>
>> PetscFunctionBegin;
>> ierr = MPI_Comm_size(((PetscObject)V)->comm,&size);CHKERRQ(ierr);
>> if (size > 1) {
>> SETERRQ(PETSC_ERR_ARG_WRONG,"Cannot create VECSEQ on more than one
>> process");
>> }
>> ierr = PetscMalloc(n*sizeof(PetscScalar),&array);CHKERRQ(ierr);
>> ierr = PetscLogObjectMemory(V, n*sizeof(PetscScalar));CHKERRQ(ierr);
>> ierr = PetscMemzero(array,n*sizeof(PetscScalar));CHKERRQ(ierr);
>> ierr = VecCreate_Seq_Private(V,array);CHKERRQ(ierr);
>> s = (Vec_Seq*)V->data;
>> s->array_allocated = array;
>> PetscFunctionReturn(0);
>> }
>>
>>
>>
>> In well-structured code, the cost of zeroing the vector is tiny and the
>> effort to track down uninitialized bugs is significant enough that this
>> seems like a sane default.
>>
>> Jed
>