Program zggsvd3_example
! ZGGSVD3 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: zggsvd3, ztrcon
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=dp) :: eps, rcond, serrbd
Integer :: i, ifail, info, irank, j, k, l, lda, ldb, ldq, ldu, ldv, &
lwork, m, n, p
! .. Local Arrays ..
Complex (Kind=dp), Allocatable :: a(:, :), b(:, :), q(:, :), u(:, :), &
v(:, :), work(:)
Complex (Kind=dp) :: wdum(1)
Real (Kind=dp), Allocatable :: alpha(:), beta(:), rwork(:)
Integer, Allocatable :: iwork(:)
Character (1) :: clabs(1), rlabs(1)
! .. Intrinsic Procedures ..
Intrinsic :: epsilon, nint, real
! .. Executable Statements ..
Write (nout, *) 'ZGGSVD3 Example Program Results'
Write (nout, *)
Flush (nout)
! Skip heading in data file
Read (nin, *)
Read (nin, *) m, n, p
lda = m
ldb = p
ldq = n
ldu = m
ldv = p
Allocate (a(lda,n), b(ldb,n), q(ldq,n), u(ldu,m), v(ldv,p), alpha(n), &
beta(n), rwork(2*n), iwork(n))
! Perform workspace query to get optimal size of work
lwork = -1
Call zggsvd3('U', 'V', 'Q', m, n, p, k, l, a, lda, b, ldb, alpha, beta, &
u, ldu, v, ldv, q, ldq, wdum, lwork, rwork, iwork, info)
lwork = nint(real(wdum(1)))
Allocate (work(lwork))
! Read the m by n matrix A and p by n matrix B from data file
Read (nin, *)(a(i,1:n), i=1, m)
Read (nin, *)(b(i,1:n), i=1, p)
! Compute the generalized singular value decomposition of (A, B)
! (A = U*D1*(0 R)*(Q**H), B = V*D2*(0 R)*(Q**H), m.ge.n)
Call zggsvd3('U', 'V', 'Q', m, n, p, k, l, a, lda, b, ldb, alpha, beta, &
u, ldu, v, ldv, q, ldq, work, lwork, rwork, iwork, info)
If (info==0) Then
! Print solution
irank = k + l
Write (nout, *) 'Number of infinite generalized singular values (K)'
Write (nout, 100) k
Write (nout, *) 'Number of finite generalized singular values (L)'
Write (nout, 100) l
Write (nout, *) 'Numerical rank of (A**T B**T)**T (K+L)'
Write (nout, 100) irank
Write (nout, *)
Write (nout, *) 'Finite generalized singular values'
Write (nout, 110)(alpha(j)/beta(j), j=k+1, irank)
Write (nout, *)
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, m, u, &
ldu, 'Bracketed', '1P,E12.4', 'Unitary matrix U', 'Integer', rlabs, &
'Integer', clabs, 80, 0, ifail)
Write (nout, *)
Flush (nout)
Call nagf_file_print_matrix_complex_gen_comp('General', ' ', p, p, v, &
ldv, 'Bracketed', '1P,E12.4', 'Unitary matrix V', 'Integer', rlabs, &
'Integer', clabs, 80, 0, ifail)
Write (nout, *)
Flush (nout)
Call nagf_file_print_matrix_complex_gen_comp('General', ' ', n, n, q, &
ldq, 'Bracketed', '1P,E12.4', 'Unitary matrix Q', 'Integer', rlabs, &
'Integer', clabs, 80, 0, ifail)
Write (nout, *)
Flush (nout)
Call nagf_file_print_matrix_complex_gen_comp('Upper triangular', &
'Non-unit', irank, irank, a(1,n-irank+1), lda, 'Bracketed', &
'1P,E12.4', 'Nonsingular upper triangular matrix R', 'Integer', &
rlabs, 'Integer', clabs, 80, 0, ifail)
! Call ZTRCON to estimate the reciprocal condition
! number of R
Call ztrcon('Infinity-norm', 'Upper', 'Non-unit', irank, &
a(1,n-irank+1), lda, rcond, work, rwork, info)
Write (nout, *)
Write (nout, *) 'Estimate of reciprocal condition number for R'
Write (nout, 120) rcond
Write (nout, *)
! So long as irank = n, get the machine precision, eps, and
! compute the approximate error bound for the computed
! generalized singular values
If (irank==n) Then
eps = epsilon(1.0E0_dp)
serrbd = eps/rcond
Write (nout, *) 'Error estimate for the generalized singular values'
Write (nout, 120) serrbd
Else
Write (nout, *) '(A**T B**T)**T is not of full rank'
End If
Else
Write (nout, 130) 'Failure in ZGGSVD3. INFO =', info
End If
100 Format (1X, I5)
110 Format (4X, 8(1P,E13.4))
120 Format (3X, 1P, E11.1)
130 Format (1X, A, I4)
End Program