! D02PSF Example Program Text
! Mark 27.1 Release. NAG Copyright 2020.
Module d02psfe_mod
! D02PSF 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 ..
Real (Kind=nag_wp), Parameter, Public :: tol0 = 1.0E-3_nag_wp
Integer, Parameter, Public :: n = 2, nin = 5, nout = 6, npts = 16, &
nwant = 1
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(*)
! .. Executable Statements ..
yp(1) = y(2)
yp(2) = -y(1)
Return
End Subroutine f
End Module d02psfe_mod
Program d02psfe
! D02PSF Example Main Program
! .. Use Statements ..
Use d02psfe_mod, Only: f, lrwsav, n, nin, nout, npts, nwant, tol0
Use nag_library, Only: d02pff, d02pqf, d02psf, d02ptf, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Local Scalars ..
Real (Kind=nag_wp) :: hnext, hstart, tend, tinc, tnow, &
tol, tstart, twant, waste
Integer :: fevals, i, ideriv, ifail, lwcomm, &
method, stepcost, stepsok
! .. Local Arrays ..
Real (Kind=nag_wp) :: ruser(1), thresh(n), yinit(n), &
ynow(n), ypnow(n), ypwant(nwant), &
ywant(nwant)
Real (Kind=nag_wp), Allocatable :: rwsav(:), wcomm(:)
Integer :: iuser(1), iwsav(130)
! .. Intrinsic Procedures ..
Intrinsic :: real
! .. Executable Statements ..
Write (nout,*) 'D02PSF Example Program Results'
! Skip heading in data file
Read (nin,*)
lwcomm = n + 5*nwant
Allocate (rwsav(lrwsav),wcomm(lwcomm))
wcomm(1:lwcomm) = 0.0_nag_wp
! Set initial conditions and input for D02PQF
Read (nin,*) method
Read (nin,*) tstart, tend
Read (nin,*) yinit(1:n)
Read (nin,*) hstart
Read (nin,*) thresh(1:n)
! Set output control
tinc = (tend-tstart)/real(npts,kind=nag_wp)
tol = tol0*10.0_nag_wp
Do i = 1, 2
tol = tol*0.1_nag_wp
! Set up integration.
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)
! Set up first point at which solution is desired.
twant = tstart + tinc
tnow = tstart
! Integrate by steps until tend is reached or error is encountered.
integ: Do While (tnow<tend)
! Integrate one step to tnow.
ifail = 0
Call d02pff(f,n,tnow,ynow,ypnow,iuser,ruser,iwsav,rwsav,ifail)
! Interpolate at required additional points up to tnow.
interp: Do While (twant<=tnow)
! Interpolate and print solution at t = twant.
ideriv = 2
ifail = 0
Call d02psf(n,twant,ideriv,nwant,ywant,ypwant,f,wcomm,lwcomm, &
iuser,ruser,iwsav,rwsav,ifail)
Write (nout,99997) twant, ywant(1), ypwant(1)
! Set next required solution point
twant = twant + tinc
End Do interp
End Do integ
! Get integration statistics.
ifail = 0
Call d02ptf(fevals,stepcost,waste,stepsok,hnext,iwsav,rwsav,ifail)
Write (nout,99996) fevals
End Do
99999 Format (/,' Calculation with TOL = ',1P,E8.1)
99998 Format (/,' t y1 y1''',/)
99997 Format (1X,F6.3,2(3X,F8.4))
99996 Format (/,' Cost of the integration in evaluations of F is',I6)
End Program d02psfe