C++ for Scientists - Technische Universität Dresden

124 CHAPTER 4. GENERIC PROGRAMMING
void insert(int r, int c, Value v)
{
assert(r < nr && c < nc);
row index.push back(r);
col index.push back(c);
data.push back(v);
}
void sort() {}
int nnz() const { return row index.size(); }
int num rows() const { return nr; }
int num cols() const { return nc; }
int begin row(int r) const
{
unsigned i= 0;
while (i < row index.size() && row index[i] < r) ++i;
return i;
}
template friend struct coo col;
template friend struct coo row;
template friend struct coo const value;
template friend struct coo value;
private:
int nr, nc;
std::vector row index, col index;
std::vector data;
};
The matrix is supposed to be sorted lexicographically (although we omitted the implementation
of the sort function for the sake of brevity). For any offset i the i th entry in each of the vectors
row index, row index and data represent row, column and value of one non-zero entry in the matrix.
The traversal over all non-zeros of the matrix can be realized with a cursor that contains just
this offset.
struct nz cursor
{
typedef int key type;
nz cursor(int offset) : offset(offset) {}
nz cursor& operator++() { offset++; return ∗this; }
nz cursor operator++(int) { nz cursor tmp(∗this); offset++; return tmp; }
key type operator∗() const { return offset; }
bool operator!=(const nz cursor& other) { return offset != other.offset; }
protected:
int offset;
};