Program f12abfe
! F12ABF Example Program Text
! Mark 27.0 Release. NAG Copyright 2019.
! .. Use Statements ..
Use nag_library, Only: dgttrf, dgttrs, dnrm2, f12aaf, f12abf, f12acf, &
f12adf, f12aef, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Real (Kind=nag_wp), Parameter :: one = 1.0_nag_wp
Real (Kind=nag_wp), Parameter :: two = 2.0_nag_wp
Integer, Parameter :: imon = 0, nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: h, rho, s, s1, s2, s3, sigmai, &
sigmar
Integer :: i, ifail, ifail1, info, irevcm, &
lcomm, ldv, licomm, n, nconv, ncv, &
nev, niter, nshift, nx
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: comm(:), d(:,:), dd(:), dl(:), &
du(:), du2(:), mx(:), resid(:), &
v(:,:), x(:)
Integer, Allocatable :: icomm(:), ipiv(:)
! .. Intrinsic Procedures ..
Intrinsic :: real
! .. Executable Statements ..
Write (nout,*) 'F12ABF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) nx, nev, ncv, rho, sigmar, sigmai
n = nx*nx
ldv = n
licomm = 140
lcomm = 3*n + 3*ncv*ncv + 6*ncv + 60
Allocate (comm(lcomm),d(ncv,3),dd(n),dl(n),du(n),du2(n),mx(n),resid(n), &
v(ldv,ncv),x(n),icomm(licomm),ipiv(n))
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call f12aaf(n,nev,ncv,icomm,licomm,comm,lcomm,ifail)
! Set the mode.
ifail = 0
Call f12adf('SHIFTED INVERSE REAL',icomm,comm,ifail)
! Construct C = A - SIGMA*I, and factorize using DGTTRF/F07CDF.
h = one/real(n+1,kind=nag_wp)
s = rho*h/two
s1 = -one - s
s2 = two - sigmar
s3 = -one + s
dl(1:n-1) = s1
dd(1:n-1) = s2
du(1:n-1) = s3
dd(n) = s2
! The NAG name equivalent of dgttrf is f07cdf
Call dgttrf(n,dl,dd,du,du2,ipiv,info)
irevcm = 0
ifail = -1
loop: Do
Call f12abf(irevcm,resid,v,ldv,x,mx,nshift,comm,icomm,ifail)
If (irevcm/=5) Then
If (irevcm==-1 .Or. irevcm==1) Then
! Perform x <--- OP*x = inv[A-SIGMA*I]*x.
! The NAG name equivalent of dgttrs is f07cef
Call dgttrs('N',n,1,dl,dd,du,du2,ipiv,x,n,info)
Else If (irevcm==4 .And. imon/=0) Then
! Output monitoring information
Call f12aef(niter,nconv,d,d(1,2),d(1,3),icomm,comm)
! The NAG name equivalent of dnrm2 is f06ejf
Write (6,99999) niter, nconv, dnrm2(nev,d(1,3),1)
End If
Else
Exit loop
End If
End Do loop
If (ifail==0) Then
! Post-Process using F12ACF to compute eigenvalues/vectors.
ifail1 = 0
Call f12acf(nconv,d,d(1,2),v,ldv,sigmar,sigmai,resid,v,ldv,comm,icomm, &
ifail1)
! Print computed eigenvalues.
Write (nout,99998) nconv
Do i = 1, nconv
Write (nout,99997) i, d(i,1), d(i,2)
End Do
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 closest to unity are:',/)
99997 Format (1X,I8,5X,'( ',F12.4,' , ',F12.4,' )')
End Program f12abfe