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Manual Reference Pages  - dprod (3)

NAME
dprod(3f) - [FORTRAN:INTRINSIC:NUMERIC] Double product function

SYNTAX
result = dprod(x, y)

DESCRIPTION
DPROD(X,Y) produces a higher DOUBLEPRECISION product of default REAL numbers X and Y.

The result has a value equal to a processor-dependent approximation to the product of X and Y. It is recommended that the processor compute the product in double precision, rather than in single precision and then converted to double precision.
X shall be default real.
Y shall be default real.
The setting of compiler options specifying REAL size can affect this function.

ARGUMENTS
X Must be of default REAL(kind=kind(0.0)) type
Y Must have the same type and kind parameters as X

RETURN VALUE
The return value is of type real(kind=kind(0.0d0)).

EXAMPLE
Sample program: 

    program demo_dprod
    use, intrinsic :: iso_fortran_env, only : real_kinds, &
    & real32, real64, real128
    implicit none
    integer,parameter :: dp=kind(0.0d0)
    real :: x = 5.2
    real :: y = 2.3
    real(kind=dp) :: dd
       dd = dprod(x,y)
       print *, dd, x*y, kind(x), kind(dd), kind(dprod(x,y))
       ! interesting comparisons
       print *, 52*23
       print *, 52*23/100.0
       print *, 52*23/100.0d0


       !! common extension is to take doubleprecision arguments
       !! and return higher precision
       bigger: block
       doubleprecision :: xx = 5.2d0
       doubleprecision :: yy = 2.3d0
       real(kind=real128) :: ddd
       !ddd = dprod(xx,yy)
       !print *, ddd, xx*yy, kind(xx), kind(ddd), kind(dprod(xx,yy))
       endblock bigger


    end program demo_dprod

STANDARD
[[FORTRAN 77]] and later

CLASS
[[Elemental procedure|Elemental function]]

dprod (3) March 11, 2021
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