Program f08lefe
! F08LEF Example Program Text
! Mark 30.0 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dgbbrd, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
Character (1), Parameter :: vect = 'B'
! .. Local Scalars ..
Integer :: i, info, j, kl, ku, ldab, ldb, ldc, &
ldpt, ldq, m, n, ncc
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: ab(:,:), b(:,:), c(:,:), d(:), e(:), &
pt(:,:), q(:,:), work(:)
! .. Intrinsic Procedures ..
Intrinsic :: abs, max, min
! .. Executable Statements ..
Write (nout,*) 'F08LEF Example Program Results'
! Skip heading in data file
Read (nin,*)
Read (nin,*) m, n, kl, ku, ncc
ldab = kl + ku + 1
ldb = m
ldc = m
ldpt = n
ldq = m
Allocate (ab(ldab,n),b(ldb,n),c(m,ncc),d(n),e(n-1),pt(ldpt,n),q(ldq,m), &
work(2*m+2*n))
! Read A from data file
Read (nin,*)((ab(ku+1+i-j,j),j=max(i-kl,1),min(i+ku,n)),i=1,m)
! Reduce A to upper bidiagonal form
! The NAG name equivalent of dgbbrd is f08lef
Call dgbbrd(vect,m,n,ncc,kl,ku,ab,ldab,d,e,q,ldq,pt,ldpt,c,ldc,work, &
info)
! Print the absolute values of bidiagonal vectors d and e.
! Any of these can differ by a sign change by combinations of sign
! changes in columns of Q and P (rows of PT).
Write (nout,*)
Write (nout,*) 'Diagonal D:'
Write (nout,99999) abs(d(1:n))
Write (nout,*)
Write (nout,*) 'Off-diagonal E:'
Write (nout,99999) abs(e(1:n-1))
99999 Format (1X,4(3X,F11.4))
End Program f08lefe