Program f07hhfe ! F07HHF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dpbrfs, dpbtrf, dpbtrs, 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 ! .. Local Scalars .. Integer :: i, ifail, info, j, kd, ldab, ldafb, & ldb, ldx, n, nrhs Character (1) :: uplo ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ab(:,:), afb(:,:), b(:,:), berr(:), & ferr(:), work(:), x(:,:) Integer, Allocatable :: iwork(:) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout,*) 'F07HHF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n, kd, nrhs ldab = kd + 1 ldafb = kd + 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),iwork(n)) ! Set A to zero to avoid referencing uninitialized elements ab(1:kd+1,1:n) = zero ! Read A and B from data file, and copy A to AFB and B to X Read (nin,*) uplo If (uplo=='U') Then Do i = 1, n Read (nin,*)(ab(kd+1+i-j,j),j=i,min(n,i+kd)) End Do Else If (uplo=='L') Then Do i = 1, n Read (nin,*)(ab(1+i-j,j),j=max(1,i-kd),i) End Do End If Read (nin,*)(b(i,1:nrhs),i=1,n) afb(1:kd+1,1:n) = ab(1:kd+1,1:n) x(1:n,1:nrhs) = b(1:n,1:nrhs) ! Factorize A in the array AFB ! The NAG name equivalent of dpbtrf is f07hdf Call dpbtrf(uplo,n,kd,afb,ldafb,info) Write (nout,*) Flush (nout) If (info==0) Then ! Compute solution in the array X ! The NAG name equivalent of dpbtrs is f07hef Call dpbtrs(uplo,n,kd,nrhs,afb,ldafb,x,ldx,info) ! Improve solution, and compute backward errors and ! estimated bounds on the forward errors ! The NAG name equivalent of dpbrfs is f07hhf Call dpbrfs(uplo,n,kd,nrhs,ab,ldab,afb,ldafb,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,*) 'A is not positive definite' End If 99999 Format ((3X,1P,7E11.1)) End Program f07hhfe