! D02PXF Example Program Text ! Mark 24 Release. NAG Copyright 2012. Module d02pxfe_mod ! D02PXF Example Program Module: ! Parameters and User-defined Routines ! .. Use Statements .. Use nag_library, Only: nag_wp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: tol1 = 1.0E-3_nag_wp Real (Kind=nag_wp), Parameter :: tol2 = 1.0E-4_nag_wp Integer, Parameter :: neq = 2, nin = 5, nout = 6, & npts = 16 Integer, Parameter :: lenwrk = 32*neq Contains Subroutine f(t,y,yp) ! .. Scalar Arguments .. Real (Kind=nag_wp), Intent (In) :: t ! .. Array Arguments .. Real (Kind=nag_wp), Intent (In) :: y(*) Real (Kind=nag_wp), Intent (Out) :: yp(*) ! .. Executable Statements .. yp(1) = y(2) yp(2) = -y(1) Return End Subroutine f End Module d02pxfe_mod Program d02pxfe ! D02PXF Example Main Program ! .. Use Statements .. Use nag_library, Only: d02pdf, d02pvf, d02pxf, d02pyf, nag_wp Use d02pxfe_mod, Only: f, lenwrk, neq, nin, nout, npts, tol1, tol2 ! .. Implicit None Statement .. Implicit None ! .. Local Scalars .. Real (Kind=nag_wp) :: hnext, hstart, tend, tinc, tnow, & tol, tstart, twant, waste Integer :: i, ifail, lenint, method, nwant, & stpcst, stpsok, totf Logical :: errass ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: thres(:), work(:), wrkint(:), & ynow(:), ypnow(:), ypwant(:), & ystart(:), ywant(:) ! .. Intrinsic Procedures .. Intrinsic :: real ! .. Executable Statements .. Write (nout,*) 'D02PXF Example Program Results' ! Skip heading in data file Read (nin,*) ! neq: number of differential equations Read (nin,*) method, nwant lenint = neq + 5*nwant Allocate (thres(neq),work(lenwrk),wrkint(lenint),ynow(neq),ypnow(neq), & ypwant(nwant),ystart(neq),ywant(nwant)) ! Set initial conditions and input for D02PVF Read (nin,*) tstart, tend Read (nin,*) ystart(1:neq) Read (nin,*) hstart Read (nin,*) thres(1:neq) Read (nin,*) errass ! Set output control tinc = (tend-tstart)/real(npts,kind=nag_wp) Do i = 1, 2 If (i==1) tol = tol1 If (i==2) tol = tol2 ! Set up integration. ifail = 0 Call d02pvf(neq,tstart,ystart,tend,tol,thres,method,'Complex Task', & errass,hstart,work,lenwrk,ifail) Write (nout,99999) tol Write (nout,99998) Write (nout,99997) tstart, ystart(1:neq) ! 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. integr8: Do If (tnow>=tend) Exit integr8 ! Integrate one step to tnow. ifail = -1 Call d02pdf(f,tnow,ynow,ypnow,work,ifail) If (ifail/=0) Exit integr8 ! Interpolate at required additional points up to tnow. interpol8: Do If (twant>tnow) Exit interpol8 ! Interpolate and print solution at t = twant. ifail = 0 Call d02pxf(twant,'Both',nwant,ywant,ypwant,f,work,wrkint,lenint, & ifail) Write (nout,99997) twant, ywant(1), ypwant(1) ! Set next required solution point twant = twant + tinc End Do interpol8 End Do integr8 ! Get integration statistics. ifail = 0 Call d02pyf(totf,stpcst,waste,stpsok,hnext,ifail) Write (nout,99996) totf End Do 99999 Format (/' Calculation with TOL = ',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 d02pxfe