Program f07bvfe ! F07BVF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: nag_wp, x04dbf, zgbrfs, zgbtrf, zgbtrs ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Complex (Kind=nag_wp), Parameter :: zero = (0.0_nag_wp,0.0_nag_wp) Integer, Parameter :: nin = 5, nout = 6 Character (1), Parameter :: trans = 'N' ! .. Local Scalars .. Integer :: i, ifail, info, j, k, kl, ku, ldab, & ldafb, ldb, ldx, n, nrhs ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: ab(:,:), afb(:,:), b(:,:), & work(:), x(:,:) Real (Kind=nag_wp), Allocatable :: berr(:), ferr(:), rwork(:) Integer, Allocatable :: ipiv(:) Character (1) :: clabs(1), rlabs(1) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout,*) 'F07BVF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n, nrhs, kl, ku ldb = n ldx = n ldab = kl + ku + 1 ldafb = 2*kl + ku + 1 Allocate (ab(ldab,n),afb(ldafb,n),b(ldb,nrhs),work(2*n),x(ldx,n), & berr(nrhs),ferr(nrhs),rwork(n),ipiv(n)) ! Set A to zero to avoid referencing uninitialized elements ab(1:kl+ku+1,1:n) = zero ! Read A and B from data file, and copy A to AFB and B to X k = ku + 1 Read (nin,*)((ab(k+i-j,j),j=max(i-kl,1),min(i+ku,n)),i=1,n) Read (nin,*)(b(i,1:nrhs),i=1,n) afb(kl+1:2*kl+ku+1,1:n) = ab(1:kl+ku+1,1:n) x(1:n,1:nrhs) = b(1:n,1:nrhs) ! Factorize A in the array AFB ! The NAG name equivalent of zgbtrf is f07brf Call zgbtrf(n,n,kl,ku,afb,ldafb,ipiv,info) Write (nout,*) Flush (nout) If (info==0) Then ! Compute solution in the array X ! The NAG name equivalent of zgbtrs is f07bsf Call zgbtrs(trans,n,kl,ku,nrhs,afb,ldafb,ipiv,x,ldx,info) ! Improve solution, and compute backward errors and ! estimated bounds on the forward errors ! The NAG name equivalent of zgbrfs is f07bvf Call zgbrfs(trans,n,kl,ku,nrhs,ab,ldab,afb,ldafb,ipiv,b,ldb,x,ldx, & ferr,berr,work,rwork,info) ! Print solution ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04dbf('General',' ',n,nrhs,x,ldx,'Bracketed','F7.4', & 'Solution(s)','Integer',rlabs,'Integer',clabs,80,0,ifail) Write (nout,*) Write (nout,*) 'Backward errors (machine-dependent)' Write (nout,99999) berr(1:nrhs) Write (nout,*) 'Estimated forward error bounds (machine-dependent)' Write (nout,99999) ferr(1:nrhs) Else Write (nout,*) 'The factor U is singular' End If 99999 Format ((5X,1P,4(E11.1,7X))) End Program f07bvfe