! D02PUF Example Program Text
! Mark 28.7 Release. NAG Copyright 2022.
Module d02pufe_mod
! D02PUF Example Program Module:
! Parameters and User-defined Routines
! .. Use Statements ..
Use nag_library, Only: nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Accessibility Statements ..
Private
Public :: f
! .. Parameters ..
Integer, Parameter, Public :: liwsav = 130, n = 4, nin = 5, &
nout = 6
Integer, Parameter, Public :: lrwsav = 350 + 32*n
Contains
Subroutine f(t,n,y,yp,iuser,ruser)
! .. Scalar Arguments ..
Real (Kind=nag_wp), Intent (In) :: t
Integer, Intent (In) :: n
! .. Array Arguments ..
Real (Kind=nag_wp), Intent (Inout) :: ruser(*)
Real (Kind=nag_wp), Intent (In) :: y(n)
Real (Kind=nag_wp), Intent (Out) :: yp(n)
Integer, Intent (Inout) :: iuser(*)
! .. Local Scalars ..
Real (Kind=nag_wp) :: r
! .. Intrinsic Procedures ..
Intrinsic :: sqrt
! .. Executable Statements ..
r = sqrt(y(1)**2+y(2)**2)
yp(1) = y(3)
yp(2) = y(4)
yp(3) = -y(1)/r**3
yp(4) = -y(2)/r**3
Return
End Subroutine f
End Module d02pufe_mod
Program d02pufe
! D02PUF Example Main Program
! .. Use Statements ..
Use d02pufe_mod, Only: f, liwsav, lrwsav, n, nin, nout
Use nag_library, Only: d02pef, d02pqf, d02ptf, d02puf, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Local Scalars ..
Real (Kind=nag_wp) :: errmax, hnext, hstart, tend, terrmx, &
tgot, tol, tstart, twant, waste
Integer :: fevals, ifail, method, stepcost, &
stepsok
! .. Local Arrays ..
Real (Kind=nag_wp) :: rmserr(n), ruser(1), thresh(n), &
ygot(n), yinit(n), ymax(n), ypgot(n)
Real (Kind=nag_wp), Allocatable :: rwsav(:)
Integer :: iuser(1)
Integer, Allocatable :: iwsav(:)
! .. Executable Statements ..
Write (nout,*) 'D02PUF Example Program Results'
Allocate (rwsav(lrwsav),iwsav(liwsav))
! Set initial conditions and input for D02PQF
! Skip heading in data file
Read (nin,*)
Read (nin,*) method
Read (nin,*) tstart, tend
Read (nin,*) yinit(1:n)
Read (nin,*) hstart, tol
Read (nin,*) thresh(1:n)
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call d02pqf(n,tstart,tend,yinit,tol,thresh,method,hstart,iwsav,rwsav, &
ifail)
Write (nout,99999) tol
Write (nout,99998)
Write (nout,99997) tstart, yinit(1:n)
twant = tend
integ: Do
ifail = -1
Call d02pef(f,n,twant,tgot,ygot,ypgot,ymax,iuser,ruser,iwsav,rwsav, &
ifail)
If (ifail<2 .Or. ifail>4) Then
Exit integ
End If
End Do integ
If (ifail==0) Then
! Print solution.
Write (nout,99997) tgot, ygot(1:n)
! Compute and print error estimates.
ifail = 0
Call d02puf(n,rmserr,errmax,terrmx,iwsav,rwsav,ifail)
Write (nout,99996) rmserr(1:n)
Write (nout,99995) errmax, terrmx
ifail = 0
Call d02ptf(fevals,stepcost,waste,stepsok,hnext,iwsav,rwsav,ifail)
Write (nout,99994) fevals
End If
99999 Format (/,' Calculation with TOL = ',E8.1)
99998 Format (/,' t y1 y2 y3 y4',/)
99997 Format (1X,F6.3,4(3X,F8.4))
99996 Format (/,' Componentwise error assessment',/,9X,4(2X,E9.2))
99995 Format (/,' Worst global error observed was ',E9.2, &
' - it occurred at T = ',F6.3)
99994 Format (/,' Cost of the integration in evaluations of F is',I6)
End Program d02pufe