Program dgbsvx_example ! DGBSVX Example Program Text ! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com ! .. Use Statements .. Use lapack_example_aux, Only: nagf_file_print_matrix_real_gen Use lapack_interfaces, Only: dgbsvx Use lapack_precision, Only: dp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=dp) :: rcond Integer :: i, ifail, info, j, k, kl, ku, ldab, ldafb, ldb, ldx, n, nrhs Character (1) :: equed ! .. Local Arrays .. Real (Kind=dp), Allocatable :: ab(:, :), afb(:, :), b(:, :), berr(:), & c(:), ferr(:), r(:), work(:), x(:, :) Integer, Allocatable :: ipiv(:), iwork(:) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout, *) 'DGBSVX Example Program Results' Write (nout, *) Flush (nout) ! Skip heading in data file Read (nin, *) Read (nin, *) n, nrhs, kl, ku ldb = n ldx = n ldab = kl + ku + 1 ldafb = ldab + kl Allocate (ab(ldab,n), afb(ldafb,n), b(ldb,nrhs), berr(nrhs), c(n), & ferr(nrhs), r(n), work(3*n), x(ldx,nrhs), ipiv(n), iwork(n)) ! Read the band matrix A and B from data file k = ku + 1 Read (nin, *)((ab(k+i-j,j),j=max(i-kl,1),min(i+ku,n)), i=1, n) Read (nin, *)(b(i,1:nrhs), i=1, n) ! Solve the equations AX = B for X Call dgbsvx('Equilibration', 'No transpose', n, kl, ku, nrhs, ab, ldab, & afb, ldafb, ipiv, equed, r, c, b, ldb, x, ldx, rcond, ferr, berr, & work, iwork, info) If ((info==0) .Or. (info==n+1)) Then ! Print solution, error bounds, condition number, the form ! of equilibration and the pivot growth factor ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call nagf_file_print_matrix_real_gen('General', ' ', n, nrhs, x, ldx, & 'Solution(s)', ifail) Write (nout, *) Write (nout, *) 'Backward errors (machine-dependent)' Write (nout, 100) berr(1:nrhs) Write (nout, *) Write (nout, *) 'Estimated forward error bounds (machine-dependent)' Write (nout, 100) ferr(1:nrhs) Write (nout, *) Write (nout, *) 'Estimate of reciprocal condition number' Write (nout, 100) rcond Write (nout, *) If (equed=='N') Then Write (nout, *) 'A has not been equilibrated' Else If (equed=='R') Then Write (nout, *) 'A has been row scaled as diag(R)*A' Else If (equed=='C') Then Write (nout, *) 'A has been column scaled as A*diag(C)' Else If (equed=='B') Then Write (nout, *) & 'A has been row and column scaled as diag(R)*A*diag(C)' End If Write (nout, *) Write (nout, *) 'Estimate of reciprocal pivot growth factor' Write (nout, 100) work(1) If (info==n+1) Then Write (nout, *) Write (nout, *) 'The matrix A is singular to working precision' End If Else Write (nout, 110) 'The (', info, ',', info, ')', & ' element of the factor U is zero' End If 100 Format ((3X,1P,7E11.1)) 110 Format (1X, A, I3, A, I3, A, A) End Program