!   G05ZRF Example Program Text

!   Mark 30.3 Release. nAG Copyright 2024.

    Program g05zrfe

!     G05ZRF Example Main Program

!     .. Use Statements ..
      Use nag_library, Only: g05zrf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6, npmax = 4
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: rho, var, xmax, xmin, ymax, ymin
      Integer                          :: approx, icorr, icount, icov2, ifail, &
                                          norm, np, pad
!     .. Local Arrays ..
      Real (Kind=nag_wp)               :: eig(3), params(npmax)
      Real (Kind=nag_wp), Allocatable  :: lam(:), xx(:), yy(:)
      Integer                          :: m(2), maxm(2), ns(2)
!     .. Executable Statements ..
      Write (nout,*) 'G05ZRF Example Program Results'
      Write (nout,*)

!     Get problem specifications from data file
      Call read_input_data(icov2,np,params,norm,var,xmin,xmax,ymin,ymax,ns,    &
        maxm,icorr,pad)

      Allocate (lam(maxm(1)*maxm(2)),xx(ns(1)),yy(ns(2)))

!     Get square roots of the eigenvalues of the embedding matrix
      ifail = 0
      Call g05zrf(ns,xmin,xmax,ymin,ymax,maxm,var,icov2,norm,np,params,pad,    &
        icorr,lam,xx,yy,m,approx,rho,icount,eig,ifail)

!     Output results
      Call display_results(approx,m,rho,eig,icount,lam)

    Contains
      Subroutine read_input_data(icov2,np,params,norm,var,xmin,xmax,ymin,ymax, &
        ns,maxm,icorr,pad)

!       .. Implicit None Statement ..
        Implicit None
!       .. Scalar Arguments ..
        Real (Kind=nag_wp), Intent (Out) :: var, xmax, xmin, ymax, ymin
        Integer, Intent (Out)          :: icorr, icov2, norm, np, pad
!       .. Array Arguments ..
        Real (Kind=nag_wp), Intent (Out) :: params(npmax)
        Integer, Intent (Out)          :: maxm(2), ns(2)
!       .. Executable Statements ..
!       Skip heading in data file
        Read (nin,*)

!       Read in covariance function number
        Read (nin,*) icov2

!       Read in number of parameters
        Read (nin,*) np

!       Read in parameters
        If (np>0) Then
          Read (nin,*) params(1:np)
        End If

!       Read in choice of norm to use
        Read (nin,*) norm

!       Read in variance of random field
        Read (nin,*) var

!       Read in domain endpoints
        Read (nin,*) xmin, xmax
        Read (nin,*) ymin, ymax

!       Read in number of sample points
        Read (nin,*) ns(1:2)

!       Read in maximum size of embedding matrix
        Read (nin,*) maxm(1:2)

!       Read in choice of scaling in case of approximation
        Read (nin,*) icorr

!       Read in choice of padding
        Read (nin,*) pad

        Return

      End Subroutine read_input_data

      Subroutine display_results(approx,m,rho,eig,icount,lam)

!       .. Implicit None Statement ..
        Implicit None
!       .. Scalar Arguments ..
        Real (Kind=nag_wp), Intent (In) :: rho
        Integer, Intent (In)           :: approx, icount
!       .. Array Arguments ..
        Real (Kind=nag_wp), Intent (In) :: eig(3)
        Integer, Intent (In)           :: m(2)
        Real (Kind=nag_wp), Intent (In) :: lam(m(1),m(2))
!       .. Local Scalars ..
        Integer                        :: i
!       .. Executable Statements ..
!       Display size of embedding matrix
        Write (nout,*)
        Write (nout,99999) 'Size of embedding matrix = ', m(1)*m(2)

!       Display approximation information if approximation used
        Write (nout,*)
        If (approx==1) Then
          Write (nout,*) 'Approximation required'
          Write (nout,*)
          Write (nout,99998) 'RHO = ', rho
          Write (nout,99997) 'EIG = ', eig(1:3)
          Write (nout,99999) 'ICOUNT = ', icount
        Else
          Write (nout,*) 'Approximation not required'
        End If

!       Display square roots of the eigenvalues of the embedding matrix
        Write (nout,*)
        Write (nout,*) 'Square roots of eigenvalues of embedding matrix:'
        Write (nout,*)
        Do i = 1, m(1)
          Write (nout,99996) lam(i,1:m(2))
        End Do

        Return

99999   Format (1X,A,I7)
99998   Format (1X,A,F10.5)
99997   Format (1X,A,3(F10.5,1X))
99996   Format (1X,8F8.4)

      End Subroutine display_results

    End Program g05zrfe