Program zpbrfs_example
! ZPBRFS Example Program Text
! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com
! .. Use Statements ..
Use lapack_example_aux, Only: nagf_file_print_matrix_complex_gen_comp
Use lapack_interfaces, Only: zpbrfs, zpbtrf, zpbtrs
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Complex (Kind=dp), Parameter :: zero = (0.0E0_dp, 0.0E0_dp)
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 ..
Complex (Kind=dp), Allocatable :: ab(:, :), afb(:, :), b(:, :), work(:), &
x(:, :)
Real (Kind=dp), Allocatable :: berr(:), ferr(:), rwork(:)
Character (1) :: clabs(1), rlabs(1)
! .. Intrinsic Procedures ..
Intrinsic :: max, min
! .. Executable Statements ..
Write (nout, *) 'ZPBRFS 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), work(2*n), x(ldx,n), &
berr(nrhs), ferr(nrhs), rwork(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
Call zpbtrf(uplo, n, kd, afb, ldafb, info)
Write (nout, *)
Flush (nout)
If (info==0) Then
! Compute solution in the array X
Call zpbtrs(uplo, n, kd, nrhs, afb, ldafb, x, ldx, info)
! Improve solution, and compute backward errors and
! estimated bounds on the forward errors
Call zpbrfs(uplo, n, kd, nrhs, ab, ldab, afb, ldafb, 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 nagf_file_print_matrix_complex_gen_comp('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, 100) berr(1:nrhs)
Write (nout, *) 'Estimated forward error bounds (machine-dependent)'
Write (nout, 100) ferr(1:nrhs)
Else
Write (nout, *) 'A is not positive definite'
End If
100 Format ((5X,1P,4(E11.1,7X)))
End Program