FUNCTION: PTRACE() PURPOSE: Returns a string that provides the current program location. KEYWORDS: OPTION: The value of the option is retained in a common block OPTION=0 : returns null string OPTION=1 : returns highest level routine name. OPTION=2 : returns highest level routine name (indented). OPTION=3 : returns all levels Usage: Generally useful for debugging code and following code execution. Example: if keyword_set(verbose) then print,ptrace(),'X=',x Written: Jan 2007, D. Larson