DS1 is stored in file: h5ex_d_extern.data
DS1:
 [   0  -1  -2  -3  -4  -5  -6]
 [   0   0   0   0   0   0   0]
 [   0   1   2   3   4   5   6]
 [   0   2   4   6   8  10  12]