NAG Library Manual, Mark 28.6
```    Program g02btfe

!     G02BTF Example Program Text

!     Mark 28.6 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: g02btf, nag_wp, x04ccf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Real (Kind=nag_wp), Parameter    :: one = 1.0_nag_wp
Real (Kind=nag_wp), Parameter    :: zero = 0.0_nag_wp
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: alpha, sw, wt
Integer                          :: i, ifail, incx, lc, m, n, nprint
Character (1)                    :: mean
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: c(:), v(:), x(:), xbar(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: mod
!     .. Executable Statements ..
Write (nout,*) 'G02BTF Example Program Results'
Write (nout,*)

!     Skip heading in data file

Read (nin,*) mean, m, n, nprint

lc = (m*m+m)/2
Allocate (x(m),xbar(m),c(lc),v(lc))

!     Elements of X are stored consecutively
incx = 1

!     Loop over each observation individually, updating the sums of squares
!     and cross-product matrix at each iteration
sw = zero
i = 0
data_lp: Do
If (ifail/=0) Then
!         Finished processing all the data
Exit data_lp
End If

i = i + 1

!       Update the sums of squares and cross-products matrix
ifail = 0
Call g02btf(mean,m,wt,x,incx,sw,xbar,c,ifail)

!       Display the results, either at the end or every NPRINT iterations
If (mod(i,nprint)==0 .Or. i==n) Then
Write (nout,*) '---------------------------------------------'
Write (nout,99999) 'Observation: ', i, '      Weight = ', wt
Write (nout,*) '---------------------------------------------'
Write (nout,*)
Write (nout,*) 'Means'
Write (nout,99998) xbar(1:m)
Write (nout,*)
Flush (nout)
ifail = 0
Call x04ccf('Upper','Non-unit',m,c,                                  &
'Sums of squares and cross-products',ifail)

!         Convert the sums of squares and cross-products to a variance matrix
If (sw>one) Then
alpha = one/(sw-one)
v(1:lc) = alpha*c(1:lc)
Write (nout,*)
Flush (nout)
ifail = 0
Call x04ccf('Upper','Non-unit',m,v,'Variance matrix',ifail)
End If
Write (nout,*)
End If
End Do data_lp

99999 Format (1X,A,I4,A,F13.4)
99998 Format (1X,4F14.4)
End Program g02btfe
```