Controls how the compiler interprets floating-point declarations
  that do not have a specified length.

  The default, /REAL_SIZE=32, defines REAL declarations, constants,
  functions, and intrinsics as REAL(KIND=4) (single precision) and
  COMPLEX declarations, constants, functions, and intrinsics as
  COMPLEX(KIND=4) (single COMPLEX).

  Specifying /REAL_SIZE=64 defines REAL declarations, constants,
  functions, and intrinsics as REAL(KIND=8) (DOUBLE PRECISION) and
  COMPLEX declarations, constants, functions, and intrinsics as
  COMPLEX(KIND=8) (DOUBLE COMPLEX).

  This also causes intrinsic functions to produce a double precision
  REAL(KIND=8) or COMPLEX(KIND=8) result instead of a single
  precision REAL(KIND=4) or COMPLEX(KIND=4) result, unless the
  argument is explicitly typed.

  For example, if you specify /REAL_SIZE=64, references to the CMPLX
  intrinsic produce DCMPLX results (COMPLEX(KIND=8)).  However, if
  the argument to CMPLX is explicitly typed as REAL(KIND=4) or
  COMPLEX(KIND=4), the resulting data type is COMPLEX(KIND=4).

  Specifying /REAL_SIZE=128 defines REAL declarations, constants,
  functions, and intrinsics as REAL(KIND=16).  It does not affect
  COMPLEX objects.