Program f08tefe ! F08TEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dpptrf, dspgst, dsptrd, dsterf, nag_wp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, info, j, n Character (1) :: uplo ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ap(:), bp(:), d(:), e(:), tau(:) ! .. Executable Statements .. Write (nout,*) 'F08TEF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n Allocate (ap(n*(n+1)/2),bp(n*(n+1)/2),d(n),e(n-1),tau(n)) ! Read A and B from data file Read (nin,*) uplo If (uplo=='U') Then Read (nin,*)((ap(i+j*(j-1)/2),j=i,n),i=1,n) Read (nin,*)((bp(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) Read (nin,*)((bp(i+(2*n-j)*(j-1)/2),j=1,i),i=1,n) End If ! Compute the Cholesky factorization of B ! The NAG name equivalent of dpptrf is f07gdf Call dpptrf(uplo,n,bp,info) Write (nout,*) If (info>0) Then Write (nout,*) 'B is not positive definite.' Else ! Reduce the problem to standard form C*y = lambda*y, storing ! the result in A ! The NAG name equivalent of dspgst is f08tef Call dspgst(1,uplo,n,ap,bp,info) ! Reduce C to tridiagonal form T = (Q**T)*C*Q ! The NAG name equivalent of dsptrd is f08gef Call dsptrd(uplo,n,ap,d,e,tau,info) ! Calculate the eigenvalues of T (same as C) ! The NAG name equivalent of dsterf is f08jff Call dsterf(n,d,e,info) If (info>0) Then Write (nout,*) 'Failure to converge.' Else ! Print eigenvalues Write (nout,*) 'Eigenvalues' Write (nout,99999) d(1:n) End If End If 99999 Format (3X,(9F8.4)) End Program f08tefe