Manual Reference Pages - dprod (3fortran)
DPROD(3) - [NUMERIC] Double precision real product
SYNOPSIS
result = dprod(x,y)
elemental function dprod(x,y)real,intent(in) :: x real,intent(in) :: y doubleprecision :: dprod
CHARACTERISTICS
The setting of compiler options specifying the size of a default real can affect this function.
o X is a default real. o Y is a default real. o the result is a doubleprecision real.
DESCRIPTION
DPROD(3) produces a doubleprecision product of default real values X and Y.
That is, it is expected to convert the arguments to double precision before multiplying, which a simple expression X*Y would not be required to do. This can be significant in specialized computations requiring high precision.
The result has a value equal to a processor-dependent approximation to the product of X and Y. Note it is recommended in the standard that the processor compute the product in double precision, rather than in single precision then converted to double precision; but is only a recommendation.
OPTIONS
o X : the multiplier o Y : the multiplicand
RESULT
The returned value of the product should have the same value as DBLE(X)*DBLE(Y).
EXAMPLES
Sample program:
program demo_dprod implicit none integer,parameter :: dp=kind(0.0d0) real :: x = 5.2 real :: y = 2.3 doubleprecision :: xx real(kind=dp) :: ddResults: (this can vary between programming environments):print *,’algebraically 5.2 x 2.3 is exactly 11.96’ print *,’as floating point values results may differ slightly:’ ! basic usage dd = dprod(x,y) print *, ’compare dprod(xy)=’,dd, & & ’to x*y=’,x*y, & & ’to dble(x)*dble(y)=’,dble(x)*dble(y)
print *,’test if an expected result is produced’ xx=-6.0d0 write(*,*)DPROD(-3.0, 2.0),xx write(*,*)merge(’PASSED’,’FAILED’,DPROD(-3.0, 2.0) == xx)
print *,’elemental’ print *, dprod( [2.3,3.4,4.5], 10.0 ) print *, dprod( [2.3,3.4,4.5], [9.8,7.6,5.4] )
end program demo_dprod
> algebraically 5.2 x 2.3 is exactly 11.96 > as floating point values results may differ slightly: > compare dprod(xy)= 11.9599993133545 to x*y= 11.96000 > to dble(x)*dble(y)= 11.9599993133545 > test if an expected result is produced > -6.00000000000000 -6.00000000000000 > PASSED > elemental > 22.9999995231628 34.0000009536743 45.0000000000000 > 22.5399999713898 25.8400004005432 24.3000004291534
STANDARD
FORTRAN 77
SEE ALSO
DBLE(3) REAL(3)
Fortran intrinsic descriptions (license: MIT) @urbanjost
| Nemo Release 3.1 | dprod (3fortran) | November 02, 2024 |
