!   P01ABF Example Program Text
!   Mark 23 Release. NAG Copyright 2011.

    MODULE p01abfe_mod

!      P01ABF Example Program Module:
!             Parameters and User-defined Routines

!      .. Use Statements ..
       USE nag_library, ONLY : nag_wp
!      .. Implicit None Statement ..
       IMPLICIT NONE
!      .. Parameters ..
       INTEGER, PARAMETER                  :: nout = 6
    CONTAINS
       SUBROUTINE mysqrt(x,y,ifail)

!         Simple routine to compute square root

!         .. Use Statements ..
          USE nag_library, ONLY : p01abf
!         .. Implicit None Statement ..
          IMPLICIT NONE
!         .. Parameters ..
          INTEGER, PARAMETER                  :: nrec = 1
          CHARACTER (6), PARAMETER            :: srname = 'MYSQRT'
!         .. Scalar Arguments ..
          REAL (KIND=nag_wp), INTENT (IN)     :: x
          REAL (KIND=nag_wp), INTENT (OUT)    :: y
          INTEGER, INTENT (INOUT)             :: ifail
!         .. Local Scalars ..
          INTEGER                             :: ierror
!         .. Local Arrays ..
          CHARACTER (51)                      :: rec(nrec)
!         .. Intrinsic Functions ..
          INTRINSIC                              sqrt
!         .. Executable Statements ..
          IF (x>=0.0_nag_wp) THEN
             y = sqrt(x)
             ifail = 0
          ELSE
             ierror = 1
             WRITE (rec,99999) '** Attempt to take the square root of ', x
             FLUSH (nout)

             ifail = p01abf(ifail,ierror,srname,nrec,rec)

          END IF

          RETURN

99999     FORMAT (1X,A,1P,E12.5)
       END SUBROUTINE mysqrt
    END MODULE p01abfe_mod
    PROGRAM p01abfe

!      P01ABF Example Main Program

!      .. Use Statements ..
       USE nag_library, ONLY : nag_wp
       USE p01abfe_mod, ONLY : mysqrt, nout
!      .. Implicit None Statement ..
       IMPLICIT NONE
!      .. Local Scalars ..
       REAL (KIND=nag_wp)                  :: y
       INTEGER                             :: ifail
!      .. Executable Statements ..
       WRITE (nout,*) 'P01ABF Example Program Results'

       WRITE (nout,*)
       WRITE (nout,*) &
          'Soft failure, silent exit - message output from the main program'

       ifail = 1
       CALL mysqrt(-1.0_nag_wp,y,ifail)

!      Must test IFAIL on exit if it is not 0 on entry

       IF (ifail==0) THEN
          WRITE (nout,99999) y
       ELSE
          WRITE (nout,*) &
             'Attempt to take the square root of a negative number'
       END IF

       WRITE (nout,*)
       WRITE (nout,*) 'Soft failure, noisy exit'

       ifail = -1
       CALL mysqrt(-2.0_nag_wp,y,ifail)

!      Must test IFAIL on exit, but now no need to display a failure message

       IF (ifail==0) THEN
          WRITE (nout,99999) y
       END IF

       WRITE (nout,*)
       WRITE (nout,*) 'Hard failure, noisy exit'

       ifail = 0
       CALL mysqrt(-3.0_nag_wp,y,ifail)

       WRITE (nout,99999) y

99999  FORMAT (1X,F10.4)
    END PROGRAM p01abfe