nag_sparse_sym_sort (f11zbc) takes a symmetric coordinate storage (SCS) representation (see the
f11 Chapter Introduction) of a real
by
sparse symmetric matrix
, and reorders the nonzero elements by increasing row index and increasing column index within each row. Entries with duplicate row and column indices may be removed, or the values may be summed. Any entries with zero values may optionally be removed.
nag_sparse_sym_sort (f11zbc) also returns
istr which contains the starting indices of each row in
.
None.
- 1:
– IntegerInput
-
On entry: the order of the matrix .
Constraint:
.
- 2:
– Integer *Input/Output
-
On entry: the number of nonzero elements in the lower triangular part of the matrix .
Constraint:
.
On exit: the number of lower triangular nonzero elements with unique row and column indices.
- 3:
– doubleInput/Output
-
On entry: the nonzero elements of the lower triangular part of the matrix . These may be in any order and there may be multiple nonzero elements with the same row and column indices.
On exit: the lower triangular nonzero elements ordered by increasing row index, and by increasing column index within each row. Each nonzero element has a unique row and column index.
- 4:
– IntegerInput/Output
-
On entry: the row indices of the elements supplied in array
a.
Constraint:
, for .
On exit: the first
nnz elements contain the row indices corresponding to the elements returned in array
a.
- 5:
– IntegerInput/Output
-
On entry: the column indices of the elements supplied in array
a
Constraint:
, for .
On exit: the first
nnz elements contain the column indices corresponding to the elements returned in array
a.
- 6:
– Nag_SparseSym_DupsInput
-
On entry: indicates how any nonzero elements with duplicate row and column indices are to be treated:
- if then duplicate elements are removed;
- if then duplicate elements are summed.
Constraint:
or .
- 7:
– Nag_SparseSym_ZerosInput
-
On entry: indicates how any elements with zero values in
a are to be treated:
- if then elements with zero value are removed;
- if then elements with zero value are kept.
Constraint:
or .
- 8:
– IntegerOutput
-
On exit:
, for
, is the starting index in the arrays
a,
irow and
icol of each row
of the matrix
.
is the index of the last nonzero element in
plus one.
- 9:
– NagError *Input/Output
-
The NAG error argument (see
Section 3.7 in How to Use the NAG Library and its Documentation).
Not applicable.
The time taken for a call to
nag_sparse_sym_sort (f11zbc) is proportional to
nnz. Note that the resulting matrix may have either rows or columns with no entries. If row
has no entries then
.
This example program reads the SCS representation of a real sparse symmetric matrix , reorders the nonzero elements, and outputs the original and the reordered representations.