NAG Library Manual, Mark 28.4
```!   M01DAF Example Program Text
!   Mark 28.4 Release. NAG Copyright 2022.

Module m01dafe_mod

!     M01DAF Example Program Module:
!       Parameters and User-defined Routines

!     .. Use Statements ..
Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Accessibility Statements ..
Private
Public                           :: ex1, ex2
!     .. Parameters ..
Integer, Parameter, Public       :: nin = 5, nout = 6
Contains

Subroutine ex1
!       Example 1: rank data in ascending order

!       .. Use Statements ..
Use nag_library, Only: m01daf
!       .. Implicit None Statement ..
Implicit None
!       .. Local Scalars ..
Integer                        :: i, ifail, m1, m2
!       .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: rv(:)
Integer, Allocatable           :: irank(:)
!       .. Executable Statements ..

Write (nout,*)
Write (nout,*)
Write (nout,*) 'Example 1'

m1 = 1

Allocate (rv(m2),irank(m2))

!       Read vector to be ranked

ifail = 0
Call m01daf(rv,m1,m2,'Ascending',irank,ifail)

Write (nout,*) '   Data   Ranks'
Write (nout,*)

Do i = m1, m2
Write (nout,99999) rv(i), irank(i)
End Do
Deallocate (rv,irank)

99999   Format (1X,F7.1,I7)

End Subroutine ex1

Subroutine ex2
!       Example 2: rank data, invert the rank permutation and calculate
!                  weighted quantiles

!       .. Use Statements ..
Use nag_library, Only: m01daf, m01naf, m01zaf
!       .. Local Scalars ..
Real (Kind=nag_wp)             :: aq
Integer                        :: i, ifail, iv, n, nq
!       .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: cwt(:), q(:), qv(:), rv(:), wt(:)
Integer, Allocatable           :: irank(:)
!       .. Executable Statements ..

Write (nout,*)
Write (nout,*)
Write (nout,*) 'Example 2'

Allocate (q(nq),rv(n),wt(n),qv(nq),irank(n),cwt(n))

!       Rank the data
ifail = 0
Call m01daf(rv,1,n,'Ascending',irank,ifail)

!       Convert ranks into indices
ifail = 0
Call m01zaf(irank,1,n,ifail)

!       Obtain the cumulative sum of the weights of the sorted data
cwt(1) = wt(irank(1))
Do i = 2, n
cwt(i) = cwt(i-1) + wt(irank(i))
End Do

!       Read in the required quantiles

!       Find the quantiles
Do i = 1, nq
!         scale the quantiles w.r.t the total cumulative sum
aq = q(i)*cwt(n)

ifail = 0
iv = m01naf(.False.,cwt,1,n,aq,ifail)

iv = iv + 1
If (iv>n) Then
iv = n
End If

!         convert the index returned by M01NAF into a value
!         from the (sorted) original data
qv(i) = rv(irank(iv))
End Do

!       Display results
Write (nout,*) 'Quantile     Result'
Write (nout,*)
Write (nout,99999)(q(i),qv(i),i=1,nq)

99999   Format (1X,F7.2,4X,F7.2)

Deallocate (q,rv,wt,qv,irank,cwt)
End Subroutine ex2

End Module m01dafe_mod
Program m01dafe
!     Mark 28.4 Release. NAG Copyright 2022.

!     M01NDF Example Main Program

!     .. Use Statements ..
Use m01dafe_mod, Only: ex1, ex2, nin, nout
!     .. Implicit None Statement ..
Implicit None
!     .. Executable Statements ..
Write (nout,*) 'M01DAF Example Program Results'

!     Skip heading in data file