A do loop iterates the code between the do and end the number of times indicated by the do statement.  So in this instance: do a=1 to &dim.; the code up to the corresponding end statement will be executed &dim. times, with the variable a being incremented by 1 on each iteration.   Modelling data is the technique of efficiently storing and using data.  There are manya ways to store data, some are faster to use but take more space, some are easier for different ways of thinking e.g. Normalised versus Transposed.  In this instance you have all the data going across the page, it is called transposed and is often associated with Excel working.  Normalised, means having a small set of variables where the data go down the page rather than across - mostly used in database and such like.  There are benefits to both, although my preference leans towards the latter.  I provided an example earlier of each:   Transposed (as you have it now) output1 output2 output3 input1 input2 input3 ...ddd1 ddd2 ddd3 1           3           2            8        9         1           12      14     13 ...   Nomalised Order   Output  Input ... ddd 1           1          8           12 2           3          9            14 3           2          1            13 ... View more