Program e02befe

!     E02BEF Example Program Text

!     Mark 27.3 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use nag_library, Only: e02bbf, e02bef, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: fp, s, txr
      Integer                          :: ifail, ioerr, j, lwrk, m, n, nest, r
      Character (1)                    :: start
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: c(:), lamda(:), sp(:), w(:), wrk(:), &
                                          x(:), y(:)
      Integer, Allocatable             :: iwrk(:)
!     .. Executable Statements ..
      Write (nout,*) 'E02BEF Example Program Results'

!     Skip heading in data file
      Read (nin,*)

!     Input the number of data points, followed by the data points (X),
!     the function values (Y) and the weights (W).

      Read (nin,*) m
      nest = m + 4
      lwrk = 4*m + 16*nest + 41
      Allocate (x(m),y(m),w(m),iwrk(nest),lamda(nest),wrk(lwrk),c(nest),       &
        sp(2*m-1))

      Do r = 1, m
        Read (nin,*) x(r), y(r), w(r)
      End Do

      start = 'C'

!     Read in successive values of S until end of data file.

data: Do
        Read (nin,*,Iostat=ioerr) s

        If (ioerr<0) Then
          Exit data
        End If

!       Determine the spline approximation.

        ifail = 0
        Call e02bef(start,m,x,y,w,s,nest,n,lamda,c,fp,wrk,lwrk,iwrk,ifail)

!       Evaluate the spline at each X point and midway between
!       X points, saving the results in SP.

        Do r = 1, m

          ifail = 0
          Call e02bbf(n,lamda,c,x(r),sp((r-1)*2+1),ifail)

        End Do

        Do r = 1, m - 1
          txr = (x(r)+x(r+1))/2.0E0_nag_wp

          ifail = 0
          Call e02bbf(n,lamda,c,txr,sp(r*2),ifail)

        End Do

!       Output the results.

        Write (nout,*)
        Write (nout,99999) 'Calling with smoothing factor S =', s
        Write (nout,*)
        Write (nout,*) '                                           B-Spline'
        Write (nout,*)                                                         &
          '             J       Knot LAMDA(J+2)   Coefficient C(J)'
        Write (nout,99998) 1, c(1)

        Do j = 2, n - 5
          Write (nout,99997) j, lamda(j+2), c(j)
        End Do

        Write (nout,99998) n - 4, c(n-4)
        Write (nout,*)
        Write (nout,99999) 'Weighted sum of squared residuals FP =', fp

        If (fp==0.0E0_nag_wp) Then
          Write (nout,*) '(The spline is an interpolating spline)'
        Else If (n==8) Then
          Write (nout,*)                                                       &
            '(The spline is the weighted least squares cubic polynomial)'
        End If

        Write (nout,*)
        start = 'W'
      End Do data

99999 Format (1X,A,1P,E12.3)
99998 Format (11X,I4,20X,F16.4)
99997 Format (11X,I4,2F18.4)
    End Program e02befe