Program f08gnfe ! F08GNF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: nag_wp, x02ajf, zhpev ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 Character (1), Parameter :: uplo = 'U' ! .. Local Scalars .. Real (Kind=nag_wp) :: eerrbd, eps Integer :: i, info, j, n ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: ap(:), work(:) Complex (Kind=nag_wp) :: dummy(1,1) Real (Kind=nag_wp), Allocatable :: rwork(:), w(:) ! .. Intrinsic Procedures .. Intrinsic :: abs, max ! .. Executable Statements .. Write (nout,*) 'F08GNF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n Allocate (ap((n*(n+1))/2),work(2*n-1),rwork(3*n-2),w(n)) ! Read the upper or lower triangular part of the matrix A from ! data file If (uplo=='U') Then Read (nin,*)((ap(i+(j*(j-1))/2),j=i,n),i=1,n) Else If (uplo=='L') Then Read (nin,*)((ap(i+((2*n-j)*(j-1))/2),j=1,i),i=1,n) End If ! Solve the Hermitian eigenvalue problem ! The NAG name equivalent of zhpev is f08gnf Call zhpev('No vectors',uplo,n,ap,w,dummy,1,work,rwork,info) If (info==0) Then ! Print solution Write (nout,*) 'Eigenvalues' Write (nout,99999) w(1:n) ! Get the machine precision, EPS and compute the approximate ! error bound for the computed eigenvalues. Note that for ! the 2-norm, max( abs(W(i)) ) = norm(A), and since the ! eigenvalues are returned in ascending order ! max( abs(W(i)) ) = max( abs(W(1)), abs(W(n))) eps = x02ajf() eerrbd = eps*max(abs(w(1)),abs(w(n))) ! Print the approximate error bound for the eigenvalues Write (nout,*) Write (nout,*) 'Error estimate for the eigenvalues' Write (nout,99998) eerrbd Else Write (nout,99997) 'Failure in ZHPEV. INFO =', info End If 99999 Format (3X,(8F8.4)) 99998 Format (4X,1P,6E11.1) 99997 Format (1X,A,I4) End Program f08gnfe