virtual void coor_extract_nonzeros(EExtractRegion extract_region, EElementUniqueness element_uniqueness, const index_type len_Aval, value_type Aval[], const index_type len_Aij, index_type Arow[], index_type Acol[], const index_type row_offset=0, const index_type col_offset=0) const =0
Extract sparse elements in a coordinate data structure.