PROGRAM f07bhfe ! F07BHF Example Program Text ! Mark 23 Release. NAG Copyright 2011. ! .. Use Statements .. USE nag_library, ONLY : dgbrfs, dgbtrf, dgbtrs, nag_wp, x04caf ! .. Implicit None Statement .. IMPLICIT NONE ! .. Parameters .. REAL (KIND=nag_wp), PARAMETER :: zero = 0.0E0_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 .. REAL (KIND=nag_wp), ALLOCATABLE :: ab(:,:), afb(:,:), b(:,:), berr(:), & ferr(:), work(:), x(:,:) INTEGER, ALLOCATABLE :: ipiv(:), iwork(:) ! .. Intrinsic Functions .. INTRINSIC max, min ! .. Executable Statements .. WRITE (nout,*) 'F07BHF Example Program Results' ! Skip heading in data file READ (nin,*) READ (nin,*) n, nrhs, kl, ku ldab = kl + ku + 1 ldafb = 2*kl + ku + 1 ldb = n ldx = n ALLOCATE (ab(ldab,n),afb(ldafb,n),b(ldb,nrhs),berr(nrhs),ferr(nrhs), & work(3*n),x(ldx,n),ipiv(n),iwork(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 dgbtrf is f07bdf CALL dgbtrf(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 dgbtrs is f07bef CALL dgbtrs(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 dgbrfs is f07bhf CALL dgbrfs(trans,n,kl,ku,nrhs,ab,ldab,afb,ldafb,ipiv,b,ldb,x,ldx, & ferr,berr,work,iwork,info) ! Print solution ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 CALL x04caf('General',' ',n,nrhs,x,ldx,'Solution(s)',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 ((3X,1P,7E11.1)) END PROGRAM f07bhfe