# Using the IDL Analyst Documentation

Each chapter of the IDL Analyst Reference Guide provides an overview of the functionality described in that chapter, along with information on the types of problems addressed by that functionality.

## Rows Versus Columns

The IDL Analyst Reference Guide uses the standard linear algebraic convention for two-dimensional arrays: “row” refers to the first index of the array and “column” refers to the second. So for a 2D array A, A(i,j) is the element in row i and column j. The PM procedure makes this easy to visualize:

a = INTARR( 4, 8 ) & a(2,5) = 1 & PM, a

IDL prints:

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 1 0 0

0 0 0 0 0 0 0 0

Note that this is the opposite of the standard image processing convention used in most IDL documentation, where “column” refers to the first index of the array and “row” refers to the second. Using the standard IDL PRINT procedure, the above array would look like this:

a = INTARR( 4, 8 ) & a(2,5) = 1 & PRINT, a

IDL Prints:

0 0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

0 0 1 0

0 0 0 0

0 0 0 0

For additional information, see “Columns, Rows, and Array Majority” (Chapter 15, Application Programming).