Adapting built-in IDL code

Many of the more compelex functions and procedures that are built into IDL are written in IDL (as I understnad it I think teh simpler ones are written in C for efficiency). This means that if the function/procedure doesn't do exactly what you want it to, you can copy the original from, for example

/nfs/env-apps-01_apps01/rsi/idl_6.2/lib

to your repositry of IDL code, call it a slightly different name and then adapt it to your needs.