c----------------------------------------------------------------------- c\BeginDoc c c\Name: sgetv0 c c\Description: c Generate a random initial residual vector for the Arnoldi process. c Force the residual vector to be in the range of the operator OP. c c\Usage: c call sgetv0 c ( IDO, BMAT, ITRY, INITV, N, J, V, LDV, RESID, RNORM, c IPNTR, WORKD, IERR ) c c\Arguments c IDO Integer. (INPUT/OUTPUT) c Reverse communication flag. IDO must be zero on the first c call to sgetv0. c ------------------------------------------------------------- c IDO = 0: first call to the reverse communication interface c IDO = -1: compute Y = OP * X where c IPNTR(1) is the pointer into WORKD for X, c IPNTR(2) is the pointer into WORKD for Y. c This is for the initialization phase to force the c starting vector into the range of OP. c IDO = 2: compute Y = B * X where c IPNTR(1) is the pointer into WORKD for X, c IPNTR(2) is the pointer into WORKD for Y. c IDO = 99: done c ------------------------------------------------------------- c c BMAT Character*1. (INPUT) c BMAT specifies the type of the matrix B in the (generalized) c eigenvalue problem A*x = lambda*B*x. c B = 'I' -> standard eigenvalue problem A*x = lambda*x c B = 'G' -> generalized eigenvalue problem A*x = lambda*B*x c c ITRY Integer. (INPUT) c ITRY counts the number of times that sgetv0 is called. c It should be set to 1 on the initial call to sgetv0. c c INITV Logical variable. (INPUT) c .TRUE. => the initial residual vector is given in RESID. c .FALSE. => generate a random initial residual vector. c c N Integer. (INPUT) c Dimension of the problem. c c J Integer. (INPUT) c Index of the residual vector to be generated, with respect to c the Arnoldi process. J > 1 in case of a "restart". c c V Real N by J array. (INPUT) c The first J-1 columns of V contain the current Arnoldi basis c if this is a "restart". c c LDV Integer. (INPUT) c Leading dimension of V exactly as declared in the calling c program. c c RESID Real array of length N. (INPUT/OUTPUT) c Initial residual vector to be generated. If RESID is c provided, force RESID into the range of the operator OP. c c RNORM Real scalar. (OUTPUT) c B-norm of the generated residual. c c IPNTR Integer array of length 3. (OUTPUT) c c WORKD Real work array of length 2*N. (REVERSE COMMUNICATION). c On exit, WORK(1:N) = B*RESID to be used in SSAITR. c c IERR Integer. (OUTPUT) c = 0: Normal exit. c = -1: Cannot generate a nontrivial restarted residual vector c in the range of the operator OP. c c\EndDoc c c----------------------------------------------------------------------- c c\BeginLib c c\Local variables: c xxxxxx real c c\References: c 1. D.C. Sorensen, "Implicit Application of Polynomial Filters in c a k-Step Arnoldi Method", SIAM J. Matr. Anal. Apps., 13 (1992), c pp 357-385. c 2. R.B. Lehoucq, "Analysis and Implementation of an Implicitly c Restarted Arnoldi Iteration", Rice University Technical Report c TR95-13, Department of Computational and Applied Mathematics. c c\Routines called: c arscnd ARPACK utility routine for timing. c svout ARPACK utility routine for vector output. c slarnv LAPACK routine for generating a random vector. c sgemv Level 2 BLAS routine for matrix vector multiplication. c scopy Level 1 BLAS that copies one vector to another. c sdot Level 1 BLAS that computes the scalar product of two vectors. c snrm2 Level 1 BLAS that computes the norm of a vector. c c\Author c Danny Sorensen Phuong Vu c Richard Lehoucq CRPC / Rice University c Dept. of Computational & Houston, Texas c Applied Mathematics c Rice University c Houston, Texas c c\SCCS Information: @(#) c FILE: getv0.F SID: 2.7 DATE OF SID: 04/07/99 RELEASE: 2 c c\EndLib c c----------------------------------------------------------------------- c subroutine sgetv0 & ( ido, bmat, itry, initv, n, j, v, ldv, resid, rnorm, & ipntr, workd, ierr ) c c %----------------------------------------------------% c | Include files for debugging and timing information | c %----------------------------------------------------% c include 'debug.h' include 'stat.h' c c %------------------% c | Scalar Arguments | c %------------------% c character bmat*1 logical initv integer ido, ierr, itry, j, ldv, n Real & rnorm c c %-----------------% c | Array Arguments | c %-----------------% c integer ipntr(3) Real & resid(n), v(ldv,j), workd(2*n) c c %------------% c | Parameters | c %------------% c Real & one, zero parameter (one = 1.0E+0, zero = 0.0E+0) c c %------------------------% c | Local Scalars & Arrays | c %------------------------% c logical first, inits, orth integer idist, iseed(4), iter, msglvl, jj Real & rnorm0 save first, iseed, inits, iter, msglvl, orth, rnorm0 c c %----------------------% c | External Subroutines | c %----------------------% c external slarnv, svout, scopy, sgemv, arscnd c c %--------------------% c | External Functions | c %--------------------% c Real & sdot, snrm2 external sdot, snrm2 c c %---------------------% c | Intrinsic Functions | c %---------------------% c intrinsic abs, sqrt c c %-----------------% c | Data Statements | c %-----------------% c data inits /.true./ c c %-----------------------% c | Executable Statements | c %-----------------------% c c c %-----------------------------------% c | Initialize the seed of the LAPACK | c | random number generator | c %-----------------------------------% c if (inits) then iseed(1) = 1 iseed(2) = 3 iseed(3) = 5 iseed(4) = 7 inits = .false. end if c if (ido .eq. 0) then c c %-------------------------------% c | Initialize timing statistics | c | & message level for debugging | c %-------------------------------% c call arscnd (t0) msglvl = mgetv0 c ierr = 0 iter = 0 first = .FALSE. orth = .FALSE. c c %-----------------------------------------------------% c | Possibly generate a random starting vector in RESID | c | Use a LAPACK random number generator used by the | c | matrix generation routines. | c | idist = 1: uniform (0,1) distribution; | c | idist = 2: uniform (-1,1) distribution; | c | idist = 3: normal (0,1) distribution; | c %-----------------------------------------------------% c if (.not.initv) then idist = 2 call slarnv (idist, iseed, n, resid) end if c c %----------------------------------------------------------% c | Force the starting vector into the range of OP to handle | c | the generalized problem when B is possibly (singular). | c %----------------------------------------------------------% c call arscnd (t2) if (itry .eq. 1) then nopx = nopx + 1 ipntr(1) = 1 ipntr(2) = n + 1 call scopy (n, resid, 1, workd, 1) ido = -1 go to 9000 else if (itry .gt. 1 .and. bmat .eq. 'G') then call scopy (n, resid, 1, workd(n + 1), 1) end if end if c c %-----------------------------------------% c | Back from computing OP*(initial-vector) | c %-----------------------------------------% c if (first) go to 20 c c %-----------------------------------------------% c | Back from computing OP*(orthogonalized-vector) | c %-----------------------------------------------% c if (orth) go to 40 c if (bmat .eq. 'G') then call arscnd (t3) tmvopx = tmvopx + (t3 - t2) end if c c %------------------------------------------------------% c | Starting vector is now in the range of OP; r = OP*r; | c | Compute B-norm of starting vector. | c %------------------------------------------------------% c call arscnd (t2) first = .TRUE. if (itry .eq. 1) call scopy (n, workd(n + 1), 1, resid, 1) if (bmat .eq. 'G') then nbx = nbx + 1 ipntr(1) = n + 1 ipntr(2) = 1 ido = 2 go to 9000 else if (bmat .eq. 'I') then call scopy (n, resid, 1, workd, 1) end if c 20 continue c if (bmat .eq. 'G') then call arscnd (t3) tmvbx = tmvbx + (t3 - t2) end if c first = .FALSE. if (bmat .eq. 'G') then rnorm0 = sdot (n, resid, 1, workd, 1) rnorm0 = sqrt(abs(rnorm0)) else if (bmat .eq. 'I') then rnorm0 = snrm2(n, resid, 1) end if rnorm = rnorm0 c c %---------------------------------------------% c | Exit if this is the very first Arnoldi step | c %---------------------------------------------% c if (j .eq. 1) go to 50 c c %---------------------------------------------------------------- c | Otherwise need to B-orthogonalize the starting vector against | c | the current Arnoldi basis using Gram-Schmidt with iter. ref. | c | This is the case where an invariant subspace is encountered | c | in the middle of the Arnoldi factorization. | c | | c | s = V^{T}*B*r; r = r - V*s; | c | | c | Stopping criteria used for iter. ref. is discussed in | c | Parlett's book, page 107 and in Gragg & Reichel TOMS paper. | c %---------------------------------------------------------------% c orth = .TRUE. 30 continue c call sgemv ('T', n, j-1, one, v, ldv, workd, 1, & zero, workd(n+1), 1) call sgemv ('N', n, j-1, -one, v, ldv, workd(n+1), 1, & one, resid, 1) c c %----------------------------------------------------------% c | Compute the B-norm of the orthogonalized starting vector | c %----------------------------------------------------------% c call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 call scopy (n, resid, 1, workd(n+1), 1) ipntr(1) = n + 1 ipntr(2) = 1 ido = 2 go to 9000 else if (bmat .eq. 'I') then call scopy (n, resid, 1, workd, 1) end if c 40 continue c if (bmat .eq. 'G') then call arscnd (t3) tmvbx = tmvbx + (t3 - t2) end if c if (bmat .eq. 'G') then rnorm = sdot (n, resid, 1, workd, 1) rnorm = sqrt(abs(rnorm)) else if (bmat .eq. 'I') then rnorm = snrm2(n, resid, 1) end if c c %--------------------------------------% c | Check for further orthogonalization. | c %--------------------------------------% c if (msglvl .gt. 2) then call svout (logfil, 1, [rnorm0], ndigit, & '_getv0: re-orthonalization ; rnorm0 is') call svout (logfil, 1, [rnorm], ndigit, & '_getv0: re-orthonalization ; rnorm is') end if c if (rnorm .gt. 0.717*rnorm0) go to 50 c iter = iter + 1 if (iter .le. 5) then c c %-----------------------------------% c | Perform iterative refinement step | c %-----------------------------------% c rnorm0 = rnorm go to 30 else c c %------------------------------------% c | Iterative refinement step "failed" | c %------------------------------------% c do 45 jj = 1, n resid(jj) = zero 45 continue rnorm = zero ierr = -1 end if c 50 continue c if (msglvl .gt. 0) then call svout (logfil, 1, [rnorm], ndigit, & '_getv0: B-norm of initial / restarted starting vector') end if if (msglvl .gt. 3) then call svout (logfil, n, resid, ndigit, & '_getv0: initial / restarted starting vector') end if ido = 99 c call arscnd (t1) tgetv0 = tgetv0 + (t1 - t0) c 9000 continue return c c %---------------% c | End of sgetv0 | c %---------------% c end