Program f08fefe ! F08FEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. 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 (correspondng 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