For a declaration such as DOUBLE COMPLEX Z, the variable Z is two REAL*8 elements contiguous in memory, interpreted as one double-width complex number.
If you do not specify the size, a default size is used.
The default size, for a declaration such as DOUBLE COMPLEX Z, can be altered by compiling with any of the options -dbl, -r8, or -xtypemap. See the discussion in Chapter 2 for details.