Editing IDL (programming language) (section)

==Overview==
IDL is [[Array programming|vectorized]], [[Numerical analysis|numerical]], and interactive, and is commonly used for interactive processing of large amounts of data (including [[image processing]]).  The syntax includes many constructs from [[Fortran]] and some from [[C (programming language)|C]].

IDL originated from early [[OpenVMS|VMS]] Fortran, and its syntax still shows its heritage:
<syntaxhighlight lang="idl">
 x = findgen(100)/10
 y = sin(x)/x
 plot,x,y
</syntaxhighlight>
The {{mono|findgen}} function in the above example returns a one-dimensional array of floating point numbers, with values equal to a series of integers starting at 0.

Note that the operation in the second line applies in a vectorized manner to the whole 100-element array created in the first line, analogous to the way general-purpose array programming languages (such as [[APL programming language|APL]], [[J programming language|J]] or [[K programming language|K]]) would do it.  This example contains a division by zero; IDL will report an [[arithmetic overflow]], and store a [[NaN]] value in the corresponding element of the {{mono|y}} array (the first one), but the other array elements will be finite.  The NaN is excluded from the visualization generated by the {{mono|plot}} command.

As with most other array programming languages, IDL is very fast at doing vector operations (sometimes as fast as a well-coded custom loop in Fortran or C) but quite slow if elements need processing individually. Hence part of the art of using IDL (or any other array programming language, for that matter) for numerically heavy computations is to make use of the built-in vector operations.