program cndrv3 c c Simple program to illustrate the idea of reverse communication c in inverse mode for a generalized complex nonsymmetric eigenvalue c problem. c c We implement example three of ex-complex.doc in DOCUMENTS directory c c\Example-3 c ... Suppose we want to solve A*x = lambda*B*x in regular mode, c where A and B are derived from the finite element discretization c of the 1-dimensional convection-diffusion operator c (d^2u/dx^2) + rho*(du/dx) c on the interval [0,1] with zero boundary condition using c piecewise linear elements. c c ... OP = inv[M]*A and B = M. c c ... Use mode 2 of CNAUPD. c c\BeginLib c c\Routines called: c cnaupd ARPACK reverse communication interface routine. c cneupd ARPACK routine that returns Ritz values and (optionally) c Ritz vectors. c cgttrf LAPACK tridiagonal factorization routine. c cgttrs LAPACK tridiagonal solve routine. c slapy2 LAPACK routine to compute sqrt(x**2+y**2) carefully. c caxpy Level 1 BLAS that computes y <- alpha*x+y. c scnrm2 Level 1 BLAS that computes the norm of a vector. c av Matrix vector multiplication routine that computes A*x. c mv Matrix vector multiplication routine that computes M*x. 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: ndrv3.F SID: 2.4 DATE OF SID: 10/18/00 RELEASE: 2 c c\Remarks c 1. None c c\EndLib c-------------------------------------------------------------------------- c c %-----------------------------% c | Define leading 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=10, maxncv=25, & ldv=maxn ) c c %--------------% c | Local Arrays | c %--------------% c integer iparam(11), ipntr(14), ipiv(maxn) logical select(maxncv) Complex & ax(maxn), mx(maxn), d(maxncv), resid(maxn), & v(ldv,maxncv), workd(3*maxn), & workev(2*maxncv), & workl(3*maxncv*maxncv+5*maxncv), & dd(maxn), dl(maxn), du(maxn), du2(maxn) Real & rwork(maxn), rd(maxncv,3) c c %---------------% c | Local Scalars | c %---------------% c character bmat*1, which*2 integer ido, n, nev, ncv, lworkl, info, ierr, j, & nconv, maxitr, ishfts, mode Complex & sigma, h Real & tol logical rvec c c %------------% c | Parameters | c %------------% c Complex & zero, one parameter (zero = (0.0E+0, 0.0E+0) , & one = (1.0E+0, 0.0E+0) ) c c %-----------------------------% c | BLAS & LAPACK routines used | c %-----------------------------% c Real & scnrm2, slapy2 external caxpy, ccopy, scnrm2, cgttrf, cgttrs, & slapy2 c c %-----------------------% c | Executable Statements | c %-----------------------% c c %----------------------------------------------------% c | The number N is the dimension of the matrix. A | c | generalized eigenvalue problem is solved (BMAT = | c | 'G'). NEV is the number of eigenvalues to be | c | approximated. The user can modify NEV, NCV, WHICH | c | to solve problems of different sizes, and to get | c | different parts of the spectrum. However, The | c | following conditions must be satisfied: | c | N <= MAXN, | c | NEV <= MAXNEV, | c | NEV + 2 <= NCV <= MAXNCV | c %----------------------------------------------------% c n = 100 nev = 4 ncv = 20 if ( n .gt. maxn ) then print *, ' ERROR with _NDRV3: N is greater than MAXN ' go to 9000 else if ( nev .gt. maxnev ) then print *, ' ERROR with _NDRV3: NEV is greater than MAXNEV ' go to 9000 else if ( ncv .gt. maxncv ) then print *, ' ERROR with _NDRV3: NCV is greater than MAXNCV ' go to 9000 end if bmat = 'G' which = 'LM' sigma = zero c c %-----------------------------------------------------% c | The matrix M is chosen to be the symmetric tri- | c | diagonal matrix with 4 on the diagonal and 1 on the | c | off diagonals. It is factored by LAPACK subroutine | c | cgttrf. | c %-----------------------------------------------------% c h = one / cmplx(n+1) do 20 j = 1, n-1 dl(j) = one*h dd(j) = (4.0E+0, 0.0E+0) *h du(j) = one*h 20 continue dd(n) = (4.0E+0, 0.0E+0) *h c call cgttrf(n, dl, dd, du, du2, ipiv, ierr) if ( ierr .ne. 0 ) then print*, ' ' print*, ' ERROR with _gttrf. ' print*, ' ' go to 9000 end if c c %-----------------------------------------------------% c | The work array WORKL is used in CNAUPD 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 CNAUPD to start the Arnoldi iteration. | c %-----------------------------------------------------% c lworkl = 3*ncv**2+5*ncv tol = 0.0 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 2 of CNAUPD is used | c | (IPARAM(7) = 2). All these options can be | c | changed by the user. For details, see the | c | documentation in CNAUPD. | c %---------------------------------------------------% c ishfts = 1 maxitr = 300 mode = 2 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 CNAUPD and take | c | actions indicated by parameter IDO until | c | either convergence is indicated or maxitr | c | has been exceeded. | c %---------------------------------------------% c call cnaupd ( ido, bmat, n, which, nev, tol, resid, ncv, & v, ldv, iparam, ipntr, workd, workl, lworkl, & rwork, info ) c if (ido .eq. -1 .or. ido .eq. 1) then c c %----------------------------------------% c | Perform y <--- OP*x = inv[M]*A*x | c | The user should supply his/her own | c | matrix vector routine and a linear | c | system solver. The matrix-vector | c | subroutine should take workd(ipntr(1)) | c | as input, and the final result should | c | be returned to workd(ipntr(2)). | c %----------------------------------------% c call av (n, workd(ipntr(1)), workd(ipntr(2))) call cgttrs('N', n, 1, dl, dd, du, du2, ipiv, & workd(ipntr(2)), n, ierr) if ( ierr .ne. 0 ) then print*, ' ' print*, ' ERROR with _gttrs. ' print*, ' ' go to 9000 end if c c %-----------------------------------------% c | L O O P B A C K to call CNAUPD again. | c %-----------------------------------------% c go to 10 c else if ( ido .eq. 2) then c c %-------------------------------------% c | Perform y <--- M*x | c | The matrix vector multiplication | c | routine should take workd(ipntr(1)) | c | as input and return the result to | c | workd(ipntr(2)). | c %-------------------------------------% c call mv (n, workd(ipntr(1)), workd(ipntr(2))) c c %-----------------------------------------% c | L O O P B A C K to call CNAUPD again. | c %-----------------------------------------% c go to 10 c 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 CNAUPD. | c %--------------------------% c print *, ' ' print *, ' Error with _naupd, info = ',info print *, ' Check the documentation of _naupd.' print *, ' ' c else c c %-------------------------------------------% c | No fatal errors occurred. | c | Post-Process using CNEUPD. | 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 cneupd ( rvec, 'A', select, d, v, ldv, sigma, & workev, bmat, n, which, nev, tol, resid, ncv, v, & ldv, iparam, ipntr, workd, workl, lworkl, rwork, & ierr ) c c %----------------------------------------------% c | Eigenvalues are returned in the one | c | dimensional array D. The corresponding | c | eigenvectors are returned in the first NCONV | c | (=IPARAM(5)) columns of the two dimensional | c | array V if requested. Otherwise, an | c | orthogonal basis for the invariant subspace | c | corresponding to the eigenvalues in D is | c | returned in V. | c %----------------------------------------------% c if ( ierr .ne. 0 ) then c c %------------------------------------% c | Error condition: | c | Check the documentation of CNEUPD. | c %------------------------------------% c print *, ' ' print *, ' Error with _neupd, info = ', ierr print *, ' Check the documentation of _neupd' print *, ' ' c else c nconv = iparam(5) do 80 j=1, nconv c c %---------------------------% c | Compute the residual norm | c | | c | || A*x - lambda*M*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 call av(n, v(1,j), ax) call mv(n, v(1,j), mx) call caxpy(n, -d(j), mx, 1, ax, 1) rd(j,1) = real (d(j)) rd(j,2) = aimag(d(j)) rd(j,3) = scnrm2(n, ax, 1) rd(j,3) = rd(j,3) / slapy2(rd(j,1),rd(j,2)) 80 continue c c %-----------------------------% c | Display computed residuals. | c %-----------------------------% c call smout(6, nconv, 3, rd, maxncv, -6, & 'Ritz values (Real, Imag) and relative residuals') c 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 *, '_NDRV3 ' 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 9000 continue c end c c========================================================================== c c matrix vector multiplication subroutine c subroutine av (n, v, w) integer n, j Complex & v(n), w(n), one, two, dd, dl, du, s, h, rho parameter (one = (1.0E+0, 0.0E+0) , & two = (2.0E+0, 0.0E+0) , & rho = (1.0E+1, 0.0E+0) ) c c Compute the matrix vector multiplication y<---A*x c where A is the stiffness matrix formed by using piecewise linear c elements on [0,1]. c h = one / cmplx(n+1) s = rho / two dd = two / h dl = -one/h - s du = -one/h + s c w(1) = dd*v(1) + du*v(2) do 10 j = 2,n-1 w(j) = dl*v(j-1) + dd*v(j) + du*v(j+1) 10 continue w(n) = dl*v(n-1) + dd*v(n) return end c------------------------------------------------------------------------ subroutine mv (n, v, w) integer n, j Complex & v(n), w(n), one, four, h parameter (one = (1.0E+0, 0.0E+0) , & four = (4.0E+0, 0.0E+0) ) c c Compute the matrix vector multiplication y<---M*x c where M is the mass matrix formed by using piecewise linear elements c on [0,1]. c w(1) = four*v(1) + one*v(2) do 10 j = 2,n-1 w(j) = one*v(j-1) + four*v(j) + one*v(j+1) 10 continue w(n) = one*v(n-1) + four*v(n) c h = one / cmplx(n+1) call cscal(n, h, w, 1) return end