program bug_142 c c Avoid taking the initial vector in the range of OP after a restart c (standard case) c c Example program to illustrate the idea of reverse communication c for a standard nonsymmetric eigenvalue problem. c c We implement example one of ex-nonsym.doc in DOCUMENTS directory c c\Example-1 c ... Suppose we want to solve A*x = lambda*x in regular mode, c where A is obtained from the standard central difference c discretization of the convection-diffusion operator c (Laplacian u) + rho*(du / dx) c on the unit square [0,1]x[0,1] with zero Dirichlet boundary c condition. c c ... OP = A and B = I. c c ... Assume "call av (nx,x,y)" computes y = A*x.c c c ... Use mode 1 of DNAUPD. c c\BeginLib c c\Routines called: c dnaupd ARPACK reverse communication interface routine. c dneupd ARPACK routine that returns Ritz values and (optionally) c Ritz vectors. c dlapy2 LAPACK routine to compute sqrt(x**2+y**2) carefully. c daxpy Level 1 BLAS that computes y <- alpha*x+y. c dnrm2 Level 1 BLAS that computes the norm of a vector. c av Matrix vector multiplication routine that computes A*x. c tv Matrix vector multiplication routine that computes T*x, c where T is a tridiagonal matrix. It is used in routine c av. c c\Author c Richard Lehoucq c Danny Sorensen c Chao Yang c Dept. of Computational & c Applied Mathematics c Rice University c Houston, Texas c c\SCCS Information: @(#) c FILE: ndrv1.F SID: 2.5 DATE OF SID: 10/17/00 RELEASE: 2 c c\Remarks c 1. None c c\EndLib c--------------------------------------------------------------------------- c c %-----------------------------% c | Define maximum dimensions | c | for all arrays. | c | MAXN: Maximum dimension | c | of the A allowed. | c | MAXNEV: Maximum NEV allowed | c | MAXNCV: Maximum NCV allowed | c %-----------------------------% c integer maxn, maxnev, maxncv, ldv parameter (maxn=256, maxnev=12, maxncv=30, ldv=maxn) c c %--------------% c | Local Arrays | c %--------------% c integer iparam(11), ipntr(14) logical select(maxncv) Double precision & ax(maxn), d(maxncv,3), resid(maxn), & v(ldv,maxncv), workd(3*maxn), & workev(3*maxncv), & workl(3*maxncv*maxncv+6*maxncv), a(maxn, maxn) c c %---------------% c | Local Scalars | c %---------------% c character bmat*1, which*2 integer ido, n, nx, nev, ncv, lworkl, info, j, & ierr, nconv, maxitr, ishfts, mode Double precision & tol, sigmar, sigmai logical first, rvec c c %------------% c | Parameters | c %------------% c Double precision & zero parameter (zero = 0.0D+0) c c %-----------------------------% c | BLAS & LAPACK routines used | c %-----------------------------% c Double precision & dlapy2, dnrm2 external dlapy2, dnrm2, daxpy c c %--------------------% c | Intrinsic function | c %--------------------% c intrinsic abs c c %-----------------------% c | Executable Statements | c %-----------------------% c c %--------------------------------------------------% c | The number NX is the number of interior points | c | in the discretization of the 2-dimensional | c | convection-diffusion operator on the unit | c | square with zero Dirichlet boundary condition. | c | The number N(=NX*NX) is the dimension of the | c | matrix. A standard eigenvalue problem is | c | solved (BMAT = 'I'). NEV is the number of | c | eigenvalues to be approximated. The user can | c | modify NX, NEV, NCV, WHICH to solve problems of | c | different sizes, and to get different parts of | c | the spectrum. However, The following | c | conditions must be satisfied: | c | N <= MAXN | c | NEV <= MAXNEV | c | NEV + 2 <= NCV <= MAXNCV | c %--------------------------------------------------% c nx = 10 n = 11 nev = 1 ncv = 11 do i = 1,n do j = 1,n a(i,j) = 0.15d0/11 end do end do do j = 2,n a(1,j) = a(1,j) + 0.85d0 end do do i = 2,n a(i,1) = (1-a(1,1))/10 end do if ( n .gt. maxn ) then print *, ' ERROR with _NDRV1: N is greater than MAXN ' go to 9000 else if ( nev .gt. maxnev ) then print *, ' ERROR with _NDRV1: NEV is greater than MAXNEV ' go to 9000 else if ( ncv .gt. maxncv ) then print *, ' ERROR with _NDRV1: NCV is greater than MAXNCV ' go to 9000 end if bmat = 'I' which = 'LM' c c %-----------------------------------------------------% c | The work array WORKL is used in DNAUPD as | c | workspace. Its dimension LWORKL is set as | c | illustrated below. The parameter TOL determines | c | the stopping criterion. If TOL<=0, machine | c | precision is used. The variable IDO is used for | c | reverse communication, and is initially set to 0. | c | Setting INFO=0 indicates that a random vector is | c | generated in DNAUPD to start the Arnoldi iteration. | c %-----------------------------------------------------% c lworkl = 3*ncv**2+6*ncv tol = zero ido = 0 info = 0 c c %---------------------------------------------------% c | This program uses exact shifts with respect to | c | the current Hessenberg matrix (IPARAM(1) = 1). | c | IPARAM(3) specifies the maximum number of Arnoldi | c | iterations allowed. Mode 1 of DNAUPD is used | c | (IPARAM(7) = 1). All these options can be changed | c | by the user. For details see the documentation in | c | DNAUPD. | c %---------------------------------------------------% c ishfts = 1 maxitr = 300 mode = 1 c iparam(1) = ishfts iparam(3) = maxitr iparam(7) = mode c c %-------------------------------------------% c | M A I N L O O P (Reverse communication) | c %-------------------------------------------% c 10 continue c c %---------------------------------------------% c | Repeatedly call the routine DNAUPD and take | c | actions indicated by parameter IDO until | c | either convergence is indicated or maxitr | c | has been exceeded. | c %---------------------------------------------% c call dnaupd ( ido, bmat, n, which, nev, tol, resid, & ncv, v, ldv, iparam, ipntr, workd, workl, lworkl, & info ) c if (ido .eq. -1 .or. ido .eq. 1) then c c %-------------------------------------------% c | Perform matrix vector multiplication | c | y <--- OP*x | c | The user should supply his/her own | c | matrix vector multiplication routine here | c | that takes workd(ipntr(1)) as the input | c | vector, and return the matrix vector | c | product to workd(ipntr(2)). | c %-------------------------------------------% c call dgemv('N',n,n,1.0d0,a,maxn, & workd(ipntr(1)),1,0.0d0,workd(ipntr(2)),1) c c %-----------------------------------------% c | L O O P B A C K to call DNAUPD again. | c %-----------------------------------------% c go to 10 c else if (ido .eq. 2) then call dcopy (n, workd(ipntr(1)), 1, workd(ipntr(2)), 1) go to 10 end if c c %----------------------------------------% c | Either we have convergence or there is | c | an error. | c %----------------------------------------% c if ( info .lt. 0 ) then c c %--------------------------% c | Error message, check the | c | documentation in DNAUPD. | c %--------------------------% c print *, ' ' print *, ' Error with _naupd, info = ', info print *, ' Check the documentation of _naupd' print *, ' ' stop 1 c else c c %-------------------------------------------% c | No fatal errors occurred. | c | Post-Process using DNEUPD. | c | | c | Computed eigenvalues may be extracted. | c | | c | Eigenvectors may also be computed now if | c | desired. (indicated by rvec = .true.) | c %-------------------------------------------% c rvec = .true. c call dneupd ( rvec, 'A', select, d, d(1,2), v, ldv, & sigmar, sigmai, workev, bmat, n, which, nev, tol, & resid, ncv, v, ldv, iparam, ipntr, workd, workl, & lworkl, ierr ) c c %-----------------------------------------------% c | The real part of the eigenvalue is returned | c | in the first column of the two dimensional | c | array D, and the imaginary part is returned | c | in the second column of D. The corresponding | c | eigenvectors are returned in the first NEV | c | columns of the two dimensional array V if | c | requested. Otherwise, an orthogonal basis | c | for the invariant subspace corresponding to | c | the eigenvalues in D is returned in V. | c %-----------------------------------------------% c if ( ierr .ne. 0) then c c %------------------------------------% c | Error condition: | c | Check the documentation of DNEUPD. | c %------------------------------------% c print *, ' ' print *, ' Error with _neupd, info = ', ierr print *, ' Check the documentation of _neupd. ' print *, ' ' c else c first = .true. nconv = iparam(5) do 20 j=1, nconv c c %---------------------------% c | Compute the residual norm | c | | c | || A*x - lambda*x || | c | | c | for the NCONV accurately | c | computed eigenvalues and | c | eigenvectors. (iparam(5) | c | indicates how many are | c | accurate to the requested | c | tolerance) | c %---------------------------% c if (d(j,2) .eq. zero) then c c %--------------------% c | Ritz value is real | c %--------------------% c call dgemv('N',n,n,1.0d0,a,maxn, & v(1,j),1,0.0d0,ax,1) call daxpy(n, -d(j,1), v(1,j), 1, ax, 1) d(j,3) = dnrm2(n, ax, 1) d(j,3) = d(j,3) / abs(d(j,1)) c else if (first) then c c %------------------------% c | Ritz value is complex. | c | Residual of one Ritz | c | value of the conjugate | c | pair is computed. | c %------------------------% c call dgemv('N',n,n,1.0d0,a,maxn, & v(1,j),1,0.0d0,ax,1) call daxpy(n, -d(j,1), v(1,j), 1, ax, 1) call daxpy(n, d(j,2), v(1,j+1), 1, ax, 1) d(j,3) = dnrm2(n, ax, 1) call dgemv('N',n,n,1.0d0,a,maxn, & v(1,j+1),1,0.0d0,ax,1) call daxpy(n, -d(j,2), v(1,j), 1, ax, 1) call daxpy(n, -d(j,1), v(1,j+1), 1, ax, 1) d(j,3) = dlapy2( d(j,3), dnrm2(n, ax, 1) ) d(j,3) = d(j,3) / dlapy2(d(j,1),d(j,2)) d(j+1,3) = d(j,3) first = .false. else first = .true. end if c 20 continue c c %-----------------------------% c | Display computed residuals. | c %-----------------------------% c call dmout(6, nconv, 3, d, maxncv, -6, & 'Ritz values (Real,Imag) and relative residuals') end if c c %-------------------------------------------% c | Print additional convergence information. | c %-------------------------------------------% c if ( info .eq. 1) then print *, ' ' print *, ' Maximum number of iterations reached.' print *, ' ' else if ( info .eq. 3) then print *, ' ' print *, ' No shifts could be applied during implicit', & ' Arnoldi update, try increasing NCV.' print *, ' ' end if c print *, ' ' print *, ' _NDRV1 ' print *, ' ====== ' print *, ' ' print *, ' Size of the matrix is ', n print *, ' The number of Ritz values requested is ', nev print *, ' The number of Arnoldi vectors generated', & ' (NCV) is ', ncv print *, ' What portion of the spectrum: ', which print *, ' The number of converged Ritz values is ', & nconv print *, ' The number of Implicit Arnoldi update', & ' iterations taken is ', iparam(3) print *, ' The number of OP*x is ', iparam(9) print *, ' The convergence criterion is ', tol print *, ' ' c end if c c %---------------------------% c | Done with program dndrv1. | c %---------------------------% c 9000 continue c end c