public int used() {
return rows * columns;
}
public static final OfflineMatrix from(Matrix matrix, Resource file) {
ResourceStream out = file.writeStream();
out.put(matrix.rowCount());
out.put(matrix.columnCount());
for (Vector row: matrix.rows())
for (Entry each: row.entries())
out.put(each.value);
out.close();
return new OfflineMatrix(file);
}