! F12FAF Example Program Text ! Mark 24 Release. NAG Copyright 2012. Module f12fafe_mod ! F12FAF 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 :: one = 1.0_nag_wp Integer, Parameter :: imon = 0, ipoint = 0, & licomm = 140, nin = 5, nout = 6 Contains Subroutine tv(nx,x,y) ! Compute the matrix vector multiplication y<---T*x where T is a nx ! by nx tridiagonal matrix. ! .. Scalar Arguments .. Integer, Intent (In) :: nx ! .. Array Arguments .. Real (Kind=nag_wp), Intent (In) :: x(nx) Real (Kind=nag_wp), Intent (Out) :: y(nx) ! .. Local Scalars .. Real (Kind=nag_wp) :: dd, dl, du Integer :: j ! .. Executable Statements .. dd = 4.0_nag_wp dl = -one du = -one y(1) = dd*x(1) + du*x(2) Do j = 2, nx - 1 y(j) = dl*x(j-1) + dd*x(j) + du*x(j+1) End Do y(nx) = dl*x(nx-1) + dd*x(nx) Return End Subroutine tv Subroutine av(nx,v,w) ! .. Use Statements .. Use nag_library, Only: daxpy, dscal ! .. Scalar Arguments .. Integer, Intent (In) :: nx ! .. Array Arguments .. Real (Kind=nag_wp), Intent (In) :: v(nx*nx) Real (Kind=nag_wp), Intent (Out) :: w(nx*nx) ! .. Local Scalars .. Real (Kind=nag_wp) :: h2 Integer :: j, lo, n ! .. Intrinsic Procedures .. Intrinsic :: real ! .. Executable Statements .. h2 = one/real((nx+1)*(nx+1),kind=nag_wp) Call tv(nx,v(1),w(1)) ! The NAG name equivalent of daxpy is f06ecf Call daxpy(nx,-one,v(nx+1),1,w(1),1) Do j = 2, nx - 1 lo = (j-1)*nx Call tv(nx,v(lo+1),w(lo+1)) Call daxpy(nx,-one,v(lo-nx+1),1,w(lo+1),1) Call daxpy(nx,-one,v(lo+nx+1),1,w(lo+1),1) End Do lo = (nx-1)*nx Call tv(nx,v(lo+1),w(lo+1)) Call daxpy(nx,-one,v(lo-nx+1),1,w(lo+1),1) n = nx*nx ! The NAG name equivalent of dscal is f06edf Call dscal(n,one/h2,w,1) Return End Subroutine av End Module f12fafe_mod Program f12fafe ! F12FAF Example Main Program ! .. Use Statements .. Use nag_library, Only: dnrm2, f12faf, f12fbf, f12fcf, f12fdf, f12fef, & nag_wp Use f12fafe_mod, Only: av, imon, ipoint, licomm, nin, nout ! .. Implicit None Statement .. Implicit None ! .. Local Scalars .. Real (Kind=nag_wp) :: sigma Integer :: ifail, irevcm, j, lcomm, ldv, n, & nconv, ncv, nev, niter, nshift, nx ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ax(:), comm(:), d(:,:), mx(:), & resid(:), v(:,:), x(:) Integer :: icomm(licomm) ! .. Executable Statements .. Write (nout,*) 'F12FAF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) nx, nev, ncv n = nx*nx ldv = n lcomm = 3*n + ncv*ncv + 8*ncv + 60 Allocate (ax(n),comm(lcomm),d(ncv,2),mx(n),resid(n),v(ldv,ncv),x(n)) ifail = 0 Call f12faf(n,nev,ncv,icomm,licomm,comm,lcomm,ifail) ifail = 0 Call f12fdf('SMALLEST MAGNITUDE',icomm,comm,ifail) ! Increase the iteration limit if required. Call f12fdf('ITERATION LIMIT=500',icomm,comm,ifail) If (ipoint==1) Then ! Use pointers to Workspace in calculating matrix vector ! products rather than interfacing through the array X. Call f12fdf('POINTERS=YES',icomm,comm,ifail) End If irevcm = 0 ifail = -1 revcm: Do Call f12fbf(irevcm,resid,v,ldv,x,mx,nshift,comm,icomm,ifail) If (irevcm==5) Then Exit revcm Else If (irevcm==-1 .Or. irevcm==1) Then ! Perform matrix vector multiplication y <--- Op*x If (ipoint==0) Then Call av(nx,x,ax) x(1:n) = ax(1:n) Else Call av(nx,comm(icomm(1)),comm(icomm(2))) End If Else If (irevcm==4 .And. imon/=0) Then ! Output monitoring information Call f12fef(niter,nconv,d,d(1,2),icomm,comm) ! The NAG name equivalent of dnrm2 is f06ejf Write (6,99999) niter, nconv, dnrm2(nev,d(1,2),1) End If End Do revcm If (ifail==0) Then ! Post-Process using F12FCF to compute eigenvalue/vectors. ifail = 0 Call f12fcf(nconv,d,v,ldv,sigma,resid,v,ldv,comm,icomm,ifail) Write (nout,99998) nconv Write (nout,99997)(j,d(j,1),j=1,nconv) End If 99999 Format (1X,'Iteration',1X,I3,', No. converged =',1X,I3,', norm o', & 'f estimates =',E16.8) 99998 Format (1X/' The ',I4,' Ritz values of smallest magnitude are:'/) 99997 Format (1X,I8,5X,F12.4) End Program f12fafe