Program f08fefe
! F08FEF Example Program Text
! Mark 26 Release. NAG Copyright 2016.
! .. Use Statements ..
Use nag_library, Only: dsytrd, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, info, lda, lwork, n
Character (1) :: uplo
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: a(:,:), d(:), e(:), tau(:), work(:)
! .. Intrinsic Procedures ..
Intrinsic :: abs
! .. Executable Statements ..
Write (nout,*) 'F08FEF Example Program Results'
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
lda = n
lwork = 64*n
Allocate (a(lda,n),d(n),e(n-1),tau(n-1),work(lwork))
! Read A from data file and copy A into C to store as a full matrix
Read (nin,*) uplo
If (uplo=='U') Then
Read (nin,*)(a(i,i:n),i=1,n)
Else If (uplo=='L') Then
Read (nin,*)(a(i,1:i),i=1,n)
End If
! Reduce A to tridiagonal form
! The NAG name equivalent of dsytrd is f08fef.
Call dsytrd(uplo,n,a,lda,d,e,tau,work,lwork,info)
If (info==0) Then
! Print the diagonal and off-diagonal of tridiagonal T.
! The absolute value of E is printed since this can vary by a change of
! sign (corresponding to multiplying through a column of Q by -1).
Write (nout,*)
Write (nout,*) &
'Diagonal and off-diagonal elements of tridiagonal form'
Write (nout,*)
Write (nout,99999) 'i', 'D', 'E'
Do i = 1, n - 1
Write (nout,99998) i, d(i), abs(e(i))
End Do
Write (nout,99998) n, d(n)
Else
Write (nout,99997) info
End If
99999 Format (5X,A,9X,A,12X,A)
99998 Format (1X,I5,2(1X,F12.5))
99997 Format (1X,'** DSYTRD/F08FEF retuned with INFO = ',I10)
End Program f08fefe