[petsc-users] question about setting elements to a matrix

[Barry Smith]

> On Oct 29, 2015, at 3:53 PM, Michael Povolotskyi <mpovolot at purdue.edu> wrote:
> 
> 
> 
> On 10/29/2015 04:50 PM, Barry Smith wrote:
>>> On Oct 29, 2015, at 3:43 PM, Michael Povolotskyi <mpovolot at purdue.edu> wrote:
>>> 
>>> Dear PETSc developers,
>>> I need to set many elements into a sparse Hermitian matrix.
>>> I'd like to do this effectively.
>>> Your documentation says that one should use MatSetValues and set as many elements at one call as possible. MatSetValues expects a 2D array of values.
>>> However, my matrix elements are computed row by row. Since the matrix is Hermitian I compute only a half of them and apply complex conjugation for the rest.
>>> Will the following procedure be effective:
>>> 1. Compute a part of the row that correspond to the lower part of the matrix
>>> 2. Set this part of the row  to the matrix with MatSetValues
>>> 3. Apply complex conjugation and compute a part of the column that corresponds to upper part of the matrix
>>> 4. Set this part of the column to the matrix with MatSetValues
>>> 5. move to the next row
>>   This is ok. But you should also be able to us the SBAIJ matrix which only stores the upper half and then you would create the diagonal and right portion of the matrix row and set that a row at a time.
>> 
>>   Barry
>> 
> Thank you.
> My matrix is not blocked. Actually there are blocks, but of different size.
> Do you I understand correctly that the only format for this is the general sparse format?

  Sorry for the confusion but you should us SBAIJ with a block size of 1. We just don't have a SAIJ format since that would be completely duplicative code with SBAIJ with a block size of 1.

  Barry

> Michael.