trouve sur la page web de D.Fanning
:
QUESTION: How do I make an IDL variable have a type "undefined"?
ANSWER: At the main IDL level you can use the IDL procedure DELVAR to
delete an IDL variable and make it undefined. Inside of procedures
and functions, I use this little program named undefine that I got
from Andrew Cool at the DSTO High Frequency Radar Division in
Adelaide, Australia.