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zungqr_example.f90
executable file
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zungqr_example.f90
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Program zungqr_example
! ZUNGQR Example Program Text
! Copyright (c) 2018, Numerical Algorithms Group (NAG Ltd.)
! For licence see
! https://github.com/numericalalgorithmsgroup/LAPACK_Examples/blob/master/LICENCE.md
! .. Use Statements ..
Use lapack_example_aux, Only: nagf_file_print_matrix_complex_gen_comp
Use lapack_interfaces, Only: zgeqrf, zungqr
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, lda, lwork, m, n
Character (30) :: title
! .. Local Arrays ..
Complex (Kind=dp), Allocatable :: a(:, :), tau(:), work(:)
Character (1) :: clabs(1), rlabs(1)
! .. Executable Statements ..
Write (nout, *) 'ZUNGQR Example Program Results'
! Skip heading in data file
Read (nin, *)
Read (nin, *) m, n
lda = m
lwork = 64*n
Allocate (a(lda,n), tau(n), work(lwork))
! Read A from data file
Read (nin, *)(a(i,1:n), i=1, m)
! Compute the QR factorization of A
Call zgeqrf(m, n, a, lda, tau, work, lwork, info)
! Form the leading N columns of Q explicitly
Call zungqr(m, n, n, a, lda, tau, work, lwork, info)
! Print the leading N columns of Q only
Write (nout, *)
Write (title, 100) n
Flush (nout)
! 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', ' ', m, n, a, &
lda, 'Bracketed', 'F7.4', title, 'Integer', rlabs, 'Integer', clabs, &
80, 0, ifail)
100 Format ('The leading ', I2, ' columns of Q')
End Program