The elements are stored in the following sequence:
X(1,1), X(2,1), X(1,2), X(2,2), X(1,3), X(2,3)
i.e. the sequence moves down each column first, then across to the next row. This column order is different from that used in some other programming languages.
The storage order may be important if you use large multi-dimensional arrays and wish to carry out some operation on all the elements of the array. It is then likely to be faster to access the array in storage order, i.e. by columns rather than rows. This means arranging loop indices with the last subscript indexed by the outer loop, and so on inwards. For example:
DOUBLE PRECISION ARRAY(100,100), SUM SUM = 0.0D0 DO 250,L = 1,100 DO 150,K = 1,100 SUM = SUM + ARRAY(K,L) 150 CONTINUE 250 CONTINUEWith the loops arranged this way around the memory locations are overhead in subscript calculations.