Re: [deal.II] Obtaining the nonzero entries in matrix

[Markus Bürg]

Hello Gennadiy,

unfortunately you have to check the value of the entries:

if (std::abs (sparse_matrix.el (i,j)) > 1e-15)
std::cout ...

Best Regards,
Markus



Am 26.08.11 14:02, schrieb Gennadiy Rishkin:

Hi

I'm trying to iterate over the nonzero entries in a matrix but the code below gives all entries including zero entries. How do I obtain the values and indexes of the nonzero entries?

The test system_matrix is from step-2 (no refinement):

 6.667e-01  0.000e+00  0.000e+00  0.000e+00
 0.000e+00  6.667e-01  0.000e+00  0.000e+00
 0.000e+00  0.000e+00  6.667e-01  0.000e+00
 0.000e+00  0.000e+00  0.000e+00  6.667e-01


    for (unsigned int i = 0; i < 1 /*system_matrix.m()*/; ++i) {

std::cout << "Row " << i << " has " << sparsity_pattern.row_length(i) << " entries." << std::endl;

SparsityPattern::row_iterator rowBegin = sparsity_pattern.row_begin(i); SparsityPattern::row_iterator rowEnd = sparsity_pattern.row_end(i);

        for ( ; rowBegin != rowEnd; ++rowBegin) {

if ( sparsity_pattern.exists( i, sparsity_pattern.column_number(i, *rowBegin) ) )

                std::cout << *rowBegin << std::endl;
        }
    }

OUTPUT:

Row 0 has 4 entries.
0
1
2
3


Gennadiy


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