M_orderpack__valmed Module

medianval(3f) - [M_orderpack:MEDIAN] Returns median VALUE.

 Recursive Function MedianVal (INVALS) Result (RES_MED)

   ${TYPE} (kind=${KIND}),  Intent (In) :: INVALS(:)
   ${TYPE} (kind=${KIND})               :: RES_MED

Where ${TYPE}(kind=${KIND}) may be

   o Real(kind=real32)
   o Real(kind=real64)
   o Integer(kind=int32)

Finds out and returns the median (((Size(INVALS)+1))/2^th value)
of INVALS.

Internally, it uses the recursive procedure described in Knuth,
The Art of Computer Programming, vol. 3, 5.3.3 .

The procedure is linear in time, and does not require to be able to
interpolate in the set as the one used in ORDERVAL(3f)/ORDERLOC(3f). It
also has better worst case behavior than ORDERVAL(3f)/ORDERLOC(3f), and
is about 20% faster in average for random uniformly distributed values.

 INVALS      input array

 RES_MED    the median value of the array INVALS

program demo_medianval
! return median value
use M_orderpack, only : medianval
implicit none
character(len=*),parameter :: g='(*(g0,1x))'
   write(*,g)'real   ',&
   medianval( [80.0,70.0,20.0,10.0,1000.0] )
   write(*,g)'integer',&
   medianval( [11, 22, 33, 44, 55, 66, 77, 88] )
   write(*,g)'double ',&
   medianval( [11.0d0, 22.0d0, 33.0d0, 66.0d0, 77.0d0, 88.0d0] )
end program demo_medianval

real    70.00000
integer 44
double  33.00000000000000

Michel Olagnon, 2000-2012

John Urban, 2022.04.16

CC0-1.0