Program f08pefe ! F08PEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dgemm, dhseqr, dlange => f06raf, nag_wp, x02ajf, & x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: alpha, beta, norm Integer :: i, ifail, info, ldc, ldd, ldh, ldz, & lwork, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: c(:,:), d(:,:), h(:,:), wi(:), & work(:), wr(:), z(:,:) ! .. Executable Statements .. Write (nout,*) 'F08PEF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n ldc = n ldd = n ldh = n ldz = n lwork = n Allocate (c(ldc,n),d(ldd,n),h(ldh,n),wi(n),work(lwork),wr(n),z(ldz,n)) ! Read H from data file Read (nin,*)(h(i,1:n),i=1,n) ! Copy H into D d(1:n,1:n) = h(1:n,1:n) ! Print Matrix H ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04caf('General',' ',n,n,h,ldh,'Matrix H',ifail) ! Calculate the eigenvalues and Schur factorization of H ! The NAG name equivalent of dhseqr is f08pef Call dhseqr('Schur form','Initialize Z',n,1,n,h,ldh,wr,wi,z,ldz,work, & lwork,info) Write (nout,*) If (info>0) Then Write (nout,*) 'Failure to converge.' Else ! Compute H - Z*T*Z^T from the factorization of A and store in matrix D ! The NAG name equivelent of dgemm is f06yaf alpha = 1.0_nag_wp beta = 0.0_nag_wp Call dgemm('N','N',n,n,n,alpha,z,ldz,h,ldh,beta,c,ldc) alpha = -1.0_nag_wp beta = 1.0_nag_wp Call dgemm('N','T',n,n,n,alpha,c,ldc,z,ldz,beta,d,ldd) ! Find norm of matrix D and print warning if it is too large ! f06raf is the NAG name equivalent of the LAPACK auxiliary dlange norm = dlange('O',ldd,n,d,ldd,work) If (norm>x02ajf()**0.8_nag_wp) Then Write (nout,*) 'Norm of H-(Z*T*Z^T) is much greater than 0.' Write (nout,*) 'Schur factorization has failed.' Else ! Print eigenvalues Write (nout,*) 'Eigenvalues' Write (nout,99999)(' (',wr(i),',',wi(i),')',i=1,n) End If End If 99999 Format (1X,A,F8.4,A,F8.4,A) End Program f08pefe