NAG Library Manual, Mark 28.4
```    Program f07gvfe

!     F07GVF Example Program Text

!     Mark 28.4 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: nag_wp, x04dbf, zpprfs, zpptrf, zpptrs
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: aplen, i, ifail, info, j, ldb, ldx,  &
n, nrhs
Character (1)                    :: uplo
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: afp(:), ap(:), b(:,:), work(:),    &
x(:,:)
Real (Kind=nag_wp), Allocatable  :: berr(:), ferr(:), rwork(:)
Character (1)                    :: clabs(1), rlabs(1)
!     .. Executable Statements ..
Write (nout,*) 'F07GVF Example Program Results'
!     Skip heading in data file
ldb = n
ldx = n
aplen = n*(n+1)/2
Allocate (afp(aplen),ap(aplen),b(ldb,nrhs),work(2*n),x(ldx,n),           &
berr(nrhs),ferr(nrhs),rwork(n))

!     Read A and B from data file, and copy A to AFP and B to X

If (uplo=='U') Then
Else If (uplo=='L') Then
End If

afp(1:aplen) = ap(1:aplen)
x(1:n,1:nrhs) = b(1:n,1:nrhs)

!     Factorize A in the array AFP
!     The NAG name equivalent of zpptrf is f07grf
Call zpptrf(uplo,n,afp,info)

Write (nout,*)
Flush (nout)
If (info==0) Then

!       Compute solution in the array X
!       The NAG name equivalent of zpptrs is f07gsf
Call zpptrs(uplo,n,nrhs,afp,x,ldx,info)

!       Improve solution, and compute backward errors and
!       estimated bounds on the forward errors

!       The NAG name equivalent of zpprfs is f07gvf
Call zpprfs(uplo,n,nrhs,ap,afp,b,ldb,x,ldx,ferr,berr,work,rwork,info)

!       Print solution

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04dbf('General',' ',n,nrhs,x,ldx,'Bracketed','F7.4',             &
'Solution(s)','Integer',rlabs,'Integer',clabs,80,0,ifail)

Write (nout,*)
Write (nout,*) 'Backward errors (machine-dependent)'
Write (nout,99999) berr(1:nrhs)
Write (nout,*) 'Estimated forward error bounds (machine-dependent)'
Write (nout,99999) ferr(1:nrhs)
Else
Write (nout,*) 'A is not positive definite'
End If

99999 Format ((5X,1P,4(E11.1,7X)))
End Program f07gvfe
```