DCmplx(X, Y)
DCmplx: COMPLEX(KIND=2) function.
X: INTEGER, REAL, or COMPLEX; scalar; INTENT(IN).
Y: INTEGER or REAL; OPTIONAL (must be omitted if X is COMPLEX); scalar; INTENT(IN).
Intrinsic groups: f2c, vxt.
Description:
If X is not type COMPLEX,
constructs a value of type COMPLEX(KIND=2) from the
real and imaginary values specified by X and
Y, respectively.
If Y is omitted, 0D0 is assumed.
If X is type COMPLEX,
converts it to type COMPLEX(KIND=2).
Although this intrinsic is not standard Fortran,
it is a popular extension offered by many compilers
that support DOUBLE COMPLEX, since it offers
the easiest way to convert to DOUBLE COMPLEX
without using Fortran 90 features (such as the KIND=
argument to the CMPLX() intrinsic).
(CMPLX(0D0, 0D0) returns a single-precision
COMPLEX result, as required by standard FORTRAN 77.
That's why so many compilers provide DCMPLX(), since
DCMPLX(0D0, 0D0) returns a DOUBLE COMPLEX
result.
Still, DCMPLX() converts even REAL*16 arguments
to their REAL*8 equivalents in most dialects of
Fortran, so neither it nor CMPLX() allow easy
construction of arbitrary-precision values without
potentially forcing a conversion involving extending or
reducing precision.
GNU Fortran provides such an intrinsic, called COMPLEX().)
See Complex Intrinsic, for information on easily constructing
a COMPLEX value of arbitrary precision from REAL
arguments.