c----------------------------------------------------------------------- c\BeginDoc c c\Name: snaitr c c\Description: c Reverse communication interface for applying NP additional steps to c a K step nonsymmetric Arnoldi factorization. c c Input: OP*V_{k} - V_{k}*H = r_{k}*e_{k}^T c c with (V_{k}^T)*B*V_{k} = I, (V_{k}^T)*B*r_{k} = 0. c c Output: OP*V_{k+p} - V_{k+p}*H = r_{k+p}*e_{k+p}^T c c with (V_{k+p}^T)*B*V_{k+p} = I, (V_{k+p}^T)*B*r_{k+p} = 0. c c where OP and B are as in snaupd. The B-norm of r_{k+p} is also c computed and returned. c c\Usage: c call snaitr c ( IDO, BMAT, N, K, NP, NB, RESID, RNORM, V, LDV, H, LDH, c IPNTR, WORKD, INFO ) c c\Arguments c IDO Integer. (INPUT/OUTPUT) c Reverse communication flag. 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 WORK for X, c IPNTR(2) is the pointer into WORK for Y. c This is for the restart phase to force the new c starting vector into the range of OP. c IDO = 1: compute Y = OP * X where c IPNTR(1) is the pointer into WORK for X, c IPNTR(2) is the pointer into WORK for Y, c IPNTR(3) is the pointer into WORK for B * X. c IDO = 2: compute Y = B * X where c IPNTR(1) is the pointer into WORK for X, c IPNTR(2) is the pointer into WORK for Y. c IDO = 99: done c ------------------------------------------------------------- c When the routine is used in the "shift-and-invert" mode, the c vector B * Q is already available and do not need to be c recompute in forming OP * Q. c c BMAT Character*1. (INPUT) c BMAT specifies the type of the matrix B that defines the c semi-inner product for the operator OP. See snaupd. c B = 'I' -> standard eigenvalue problem A*x = lambda*x c B = 'G' -> generalized eigenvalue problem A*x = lambda*M**x c c N Integer. (INPUT) c Dimension of the eigenproblem. c c K Integer. (INPUT) c Current size of V and H. c c NP Integer. (INPUT) c Number of additional Arnoldi steps to take. c c NB Integer. (INPUT) c Blocksize to be used in the recurrence. c Only work for NB = 1 right now. The goal is to have a c program that implement both the block and non-block method. c c RESID Real array of length N. (INPUT/OUTPUT) c On INPUT: RESID contains the residual vector r_{k}. c On OUTPUT: RESID contains the residual vector r_{k+p}. c c RNORM Real scalar. (INPUT/OUTPUT) c B-norm of the starting residual on input. c B-norm of the updated residual r_{k+p} on output. c c V Real N by K+NP array. (INPUT/OUTPUT) c On INPUT: V contains the Arnoldi vectors in the first K c columns. c On OUTPUT: V contains the new NP Arnoldi vectors in the next c NP columns. The first K columns are unchanged. c c LDV Integer. (INPUT) c Leading dimension of V exactly as declared in the calling c program. c c H Real (K+NP) by (K+NP) array. (INPUT/OUTPUT) c H is used to store the generated upper Hessenberg matrix. c c LDH Integer. (INPUT) c Leading dimension of H exactly as declared in the calling c program. c c IPNTR Integer array of length 3. (OUTPUT) c Pointer to mark the starting locations in the WORK for c vectors used by the Arnoldi iteration. c ------------------------------------------------------------- c IPNTR(1): pointer to the current operand vector X. c IPNTR(2): pointer to the current result vector Y. c IPNTR(3): pointer to the vector B * X when used in the c shift-and-invert mode. X is the current operand. c ------------------------------------------------------------- c c WORKD Real work array of length 3*N. (REVERSE COMMUNICATION) c Distributed array to be used in the basic Arnoldi iteration c for reverse communication. The calling program should not c use WORKD as temporary workspace during the iteration !!!!!! c On input, WORKD(1:N) = B*RESID and is used to save some c computation at the first step. c c INFO Integer. (OUTPUT) c = 0: Normal exit. c > 0: Size of the spanning invariant subspace of OP found. 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 sgetv0 ARPACK routine to generate the initial vector. c ivout ARPACK utility routine that prints integers. c arscnd ARPACK utility routine for timing. c smout ARPACK utility routine that prints matrices c svout ARPACK utility routine that prints vectors. c slabad LAPACK routine that computes machine constants. c slamch LAPACK routine that determines machine constants. c slascl LAPACK routine for careful scaling of a matrix. c slanhs LAPACK routine that computes various norms of a matrix. c sgemv Level 2 BLAS routine for matrix vector multiplication. c saxpy Level 1 BLAS that computes a vector triad. c sscal Level 1 BLAS that scales a vector. 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\Revision history: c xx/xx/92: Version ' 2.4' c c\SCCS Information: @(#) c FILE: naitr.F SID: 2.4 DATE OF SID: 8/27/96 RELEASE: 2 c c\Remarks c The algorithm implemented is: c c restart = .false. c Given V_{k} = [v_{1}, ..., v_{k}], r_{k}; c r_{k} contains the initial residual vector even for k = 0; c Also assume that rnorm = || B*r_{k} || and B*r_{k} are already c computed by the calling program. c c betaj = rnorm ; p_{k+1} = B*r_{k} ; c For j = k+1, ..., k+np Do c 1) if ( betaj < tol ) stop or restart depending on j. c ( At present tol is zero ) c if ( restart ) generate a new starting vector. c 2) v_{j} = r(j-1)/betaj; V_{j} = [V_{j-1}, v_{j}]; c p_{j} = p_{j}/betaj c 3) r_{j} = OP*v_{j} where OP is defined as in snaupd c For shift-invert mode p_{j} = B*v_{j} is already available. c wnorm = || OP*v_{j} || c 4) Compute the j-th step residual vector. c w_{j} = V_{j}^T * B * OP * v_{j} c r_{j} = OP*v_{j} - V_{j} * w_{j} c H(:,j) = w_{j}; c H(j,j-1) = rnorm c rnorm = || r_(j) || c If (rnorm > 0.717*wnorm) accept step and go back to 1) c 5) Re-orthogonalization step: c s = V_{j}'*B*r_{j} c r_{j} = r_{j} - V_{j}*s; rnorm1 = || r_{j} || c alphaj = alphaj + s_{j}; c 6) Iterative refinement step: c If (rnorm1 > 0.717*rnorm) then c rnorm = rnorm1 c accept step and go back to 1) c Else c rnorm = rnorm1 c If this is the first time in step 6), go to 5) c Else r_{j} lies in the span of V_{j} numerically. c Set r_{j} = 0 and rnorm = 0; go to 1) c EndIf c End Do c c\EndLib c c----------------------------------------------------------------------- c subroutine snaitr & (ido, bmat, n, k, np, nb, resid, rnorm, v, ldv, h, ldh, & ipntr, workd, info) 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 integer ido, info, k, ldh, ldv, n, nb, np Real & rnorm c c %-----------------% c | Array Arguments | c %-----------------% c integer ipntr(3) Real & h(ldh,k+np), resid(n), v(ldv,k+np), workd(3*n) c c %------------% c | Parameters | c %------------% c Real & one, zero parameter (one = 1.0E+0, zero = 0.0E+0) c c %---------------% c | Local Scalars | c %---------------% c logical first, orth1, orth2, rstart, step3, step4 integer ierr, i, infol, ipj, irj, ivj, iter, itry, j, msglvl, & jj Real & betaj, ovfl, temp1, rnorm1, smlnum, tst1, ulp, unfl, & wnorm save first, orth1, orth2, rstart, step3, step4, & ierr, ipj, irj, ivj, iter, itry, j, msglvl, ovfl, & betaj, rnorm1, smlnum, ulp, unfl, wnorm c c %-----------------------% c | Local Array Arguments | c %-----------------------% c Real & xtemp(2) c c %----------------------% c | External Subroutines | c %----------------------% c external saxpy, scopy, sscal, sgemv, sgetv0, slabad, & svout, smout, ivout, arscnd c c %--------------------% c | External Functions | c %--------------------% c Real & sdot, snrm2, slanhs, slamch external sdot, snrm2, slanhs, slamch c c %---------------------% c | Intrinsic Functions | c %---------------------% c intrinsic abs, sqrt c c %-----------------% c | Data statements | c %-----------------% c data first / .true. / c c %-----------------------% c | Executable Statements | c %-----------------------% c if (first) then c c %-----------------------------------------% c | Set machine-dependent constants for the | c | the splitting and deflation criterion. | c | If norm(H) <= sqrt(OVFL), | c | overflow should not occur. | c | REFERENCE: LAPACK subroutine slahqr | c %-----------------------------------------% c unfl = slamch( 'safe minimum' ) ovfl = one / unfl call slabad( unfl, ovfl ) ulp = slamch( 'precision' ) smlnum = unfl*( n / ulp ) first = .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 = mnaitr c c %------------------------------% c | Initial call to this routine | c %------------------------------% c info = 0 step3 = .false. step4 = .false. rstart = .false. orth1 = .false. orth2 = .false. j = k + 1 ipj = 1 irj = ipj + n ivj = irj + n end if c c %-------------------------------------------------% c | When in reverse communication mode one of: | c | STEP3, STEP4, ORTH1, ORTH2, RSTART | c | will be .true. when .... | c | STEP3: return from computing OP*v_{j}. | c | STEP4: return from computing B-norm of OP*v_{j} | c | ORTH1: return from computing B-norm of r_{j+1} | c | ORTH2: return from computing B-norm of | c | correction to the residual vector. | c | RSTART: return from OP computations needed by | c | sgetv0. | c %-------------------------------------------------% c if (step3) go to 50 if (step4) go to 60 if (orth1) go to 70 if (orth2) go to 90 if (rstart) go to 30 c c %-----------------------------% c | Else this is the first step | c %-----------------------------% c c %--------------------------------------------------------------% c | | c | A R N O L D I I T E R A T I O N L O O P | c | | c | Note: B*r_{j-1} is already in WORKD(1:N)=WORKD(IPJ:IPJ+N-1) | c %--------------------------------------------------------------% 1000 continue c if (msglvl .gt. 1) then call ivout (logfil, 1, [j], ndigit, & '_naitr: generating Arnoldi vector number') call svout (logfil, 1, [rnorm], ndigit, & '_naitr: B-norm of the current residual is') end if c c %---------------------------------------------------% c | STEP 1: Check if the B norm of j-th residual | c | vector is zero. Equivalent to determining whether | c | an exact j-step Arnoldi factorization is present. | c %---------------------------------------------------% c betaj = rnorm if (rnorm .gt. zero) go to 40 c c %---------------------------------------------------% c | Invariant subspace found, generate a new starting | c | vector which is orthogonal to the current Arnoldi | c | basis and continue the iteration. | c %---------------------------------------------------% c if (msglvl .gt. 0) then call ivout (logfil, 1, [j], ndigit, & '_naitr: ****** RESTART AT STEP ******') end if c c %---------------------------------------------% c | ITRY is the loop variable that controls the | c | maximum amount of times that a restart is | c | attempted. NRSTRT is used by stat.h | c %---------------------------------------------% c betaj = zero nrstrt = nrstrt + 1 itry = 1 20 continue rstart = .true. ido = 0 30 continue c c %--------------------------------------% c | If in reverse communication mode and | c | RSTART = .true. flow returns here. | c %--------------------------------------% c call sgetv0 (ido, bmat, itry, .false., n, j, v, ldv, & resid, rnorm, ipntr, workd, ierr) if (ido .ne. 99) go to 9000 if (ierr .lt. 0) then itry = itry + 1 if (itry .le. 3) go to 20 c c %------------------------------------------------% c | Give up after several restart attempts. | c | Set INFO to the size of the invariant subspace | c | which spans OP and exit. | c %------------------------------------------------% c info = j - 1 call arscnd (t1) tnaitr = tnaitr + (t1 - t0) ido = 99 go to 9000 end if c 40 continue c c %---------------------------------------------------------% c | STEP 2: v_{j} = r_{j-1}/rnorm and p_{j} = p_{j}/rnorm | c | Note that p_{j} = B*r_{j-1}. In order to avoid overflow | c | when reciprocating a small RNORM, test against lower | c | machine bound. | c %---------------------------------------------------------% c call scopy (n, resid, 1, v(1,j), 1) if (rnorm .ge. unfl) then temp1 = one / rnorm call sscal (n, temp1, v(1,j), 1) call sscal (n, temp1, workd(ipj), 1) else c c %-----------------------------------------% c | To scale both v_{j} and p_{j} carefully | c | use LAPACK routine SLASCL | c %-----------------------------------------% c call slascl ('General', i, i, rnorm, one, n, 1, & v(1,j), n, infol) call slascl ('General', i, i, rnorm, one, n, 1, & workd(ipj), n, infol) end if c c %------------------------------------------------------% c | STEP 3: r_{j} = OP*v_{j}; Note that p_{j} = B*v_{j} | c | Note that this is not quite yet r_{j}. See STEP 4 | c %------------------------------------------------------% c step3 = .true. nopx = nopx + 1 call arscnd (t2) call scopy (n, v(1,j), 1, workd(ivj), 1) ipntr(1) = ivj ipntr(2) = irj ipntr(3) = ipj ido = 1 c c %-----------------------------------% c | Exit in order to compute OP*v_{j} | c %-----------------------------------% c go to 9000 50 continue c c %----------------------------------% c | Back from reverse communication; | c | WORKD(IRJ:IRJ+N-1) := OP*v_{j} | c | if step3 = .true. | c %----------------------------------% c call arscnd (t3) tmvopx = tmvopx + (t3 - t2) step3 = .false. c c %------------------------------------------% c | Put another copy of OP*v_{j} into RESID. | c %------------------------------------------% c call scopy (n, workd(irj), 1, resid, 1) c c %---------------------------------------% c | STEP 4: Finish extending the Arnoldi | c | factorization to length j. | c %---------------------------------------% c call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 step4 = .true. ipntr(1) = irj ipntr(2) = ipj ido = 2 c c %-------------------------------------% c | Exit in order to compute B*OP*v_{j} | c %-------------------------------------% c go to 9000 else if (bmat .eq. 'I') then call scopy (n, resid, 1, workd(ipj), 1) end if 60 continue c c %----------------------------------% c | Back from reverse communication; | c | WORKD(IPJ:IPJ+N-1) := B*OP*v_{j} | c | if step4 = .true. | c %----------------------------------% c if (bmat .eq. 'G') then call arscnd (t3) tmvbx = tmvbx + (t3 - t2) end if c step4 = .false. c c %-------------------------------------% c | The following is needed for STEP 5. | c | Compute the B-norm of OP*v_{j}. | c %-------------------------------------% c if (bmat .eq. 'G') then wnorm = sdot (n, resid, 1, workd(ipj), 1) wnorm = sqrt(abs(wnorm)) else if (bmat .eq. 'I') then wnorm = snrm2(n, resid, 1) end if c c %-----------------------------------------% c | Compute the j-th residual corresponding | c | to the j step factorization. | c | Use Classical Gram Schmidt and compute: | c | w_{j} <- V_{j}^T * B * OP * v_{j} | c | r_{j} <- OP*v_{j} - V_{j} * w_{j} | c %-----------------------------------------% c c c %------------------------------------------% c | Compute the j Fourier coefficients w_{j} | c | WORKD(IPJ:IPJ+N-1) contains B*OP*v_{j}. | c %------------------------------------------% c call sgemv ('T', n, j, one, v, ldv, workd(ipj), 1, & zero, h(1,j), 1) c c %--------------------------------------% c | Orthogonalize r_{j} against V_{j}. | c | RESID contains OP*v_{j}. See STEP 3. | c %--------------------------------------% c call sgemv ('N', n, j, -one, v, ldv, h(1,j), 1, & one, resid, 1) c if (j .gt. 1) h(j,j-1) = betaj c call arscnd (t4) c orth1 = .true. c call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 call scopy (n, resid, 1, workd(irj), 1) ipntr(1) = irj ipntr(2) = ipj ido = 2 c c %----------------------------------% c | Exit in order to compute B*r_{j} | c %----------------------------------% c go to 9000 else if (bmat .eq. 'I') then call scopy (n, resid, 1, workd(ipj), 1) end if 70 continue c c %---------------------------------------------------% c | Back from reverse communication if ORTH1 = .true. | c | WORKD(IPJ:IPJ+N-1) := B*r_{j}. | c %---------------------------------------------------% c if (bmat .eq. 'G') then call arscnd (t3) tmvbx = tmvbx + (t3 - t2) end if c orth1 = .false. c c %------------------------------% c | Compute the B-norm of r_{j}. | c %------------------------------% c if (bmat .eq. 'G') then rnorm = sdot (n, resid, 1, workd(ipj), 1) rnorm = sqrt(abs(rnorm)) else if (bmat .eq. 'I') then rnorm = snrm2(n, resid, 1) end if c c %-----------------------------------------------------------% c | STEP 5: Re-orthogonalization / Iterative refinement phase | c | Maximum NITER_ITREF tries. | c | | c | s = V_{j}^T * B * r_{j} | c | r_{j} = r_{j} - V_{j}*s | c | alphaj = alphaj + s_{j} | c | | c | The stopping criteria used for iterative refinement is | c | discussed in Parlett's book SEP, page 107 and in Gragg & | c | Reichel ACM TOMS paper; Algorithm 686, Dec. 1990. | c | Determine if we need to correct the residual. The goal is | c | to enforce ||v(:,1:j)^T * r_{j}|| .le. eps * || r_{j} || | c | The following test determines whether the sine of the | c | angle between OP*x and the computed residual is less | c | than or equal to 0.717. | c %-----------------------------------------------------------% c if (rnorm .gt. 0.717*wnorm) go to 100 iter = 0 nrorth = nrorth + 1 c c %---------------------------------------------------% c | Enter the Iterative refinement phase. If further | c | refinement is necessary, loop back here. The loop | c | variable is ITER. Perform a step of Classical | c | Gram-Schmidt using all the Arnoldi vectors V_{j} | c %---------------------------------------------------% c 80 continue c if (msglvl .gt. 2) then xtemp(1) = wnorm xtemp(2) = rnorm call svout (logfil, 2, xtemp, ndigit, & '_naitr: re-orthonalization; wnorm and rnorm are') call svout (logfil, j, h(1,j), ndigit, & '_naitr: j-th column of H') end if c c %----------------------------------------------------% c | Compute V_{j}^T * B * r_{j}. | c | WORKD(IRJ:IRJ+J-1) = v(:,1:J)'*WORKD(IPJ:IPJ+N-1). | c %----------------------------------------------------% c call sgemv ('T', n, j, one, v, ldv, workd(ipj), 1, & zero, workd(irj), 1) c c %---------------------------------------------% c | Compute the correction to the residual: | c | r_{j} = r_{j} - V_{j} * WORKD(IRJ:IRJ+J-1). | c | The correction to H is v(:,1:J)*H(1:J,1:J) | c | + v(:,1:J)*WORKD(IRJ:IRJ+J-1)*e'_j. | c %---------------------------------------------% c call sgemv ('N', n, j, -one, v, ldv, workd(irj), 1, & one, resid, 1) call saxpy (j, one, workd(irj), 1, h(1,j), 1) c orth2 = .true. call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 call scopy (n, resid, 1, workd(irj), 1) ipntr(1) = irj ipntr(2) = ipj ido = 2 c c %-----------------------------------% c | Exit in order to compute B*r_{j}. | c | r_{j} is the corrected residual. | c %-----------------------------------% c go to 9000 else if (bmat .eq. 'I') then call scopy (n, resid, 1, workd(ipj), 1) end if 90 continue c c %---------------------------------------------------% c | Back from reverse communication if ORTH2 = .true. | c %---------------------------------------------------% c if (bmat .eq. 'G') then call arscnd (t3) tmvbx = tmvbx + (t3 - t2) end if c c %-----------------------------------------------------% c | Compute the B-norm of the corrected residual r_{j}. | c %-----------------------------------------------------% c if (bmat .eq. 'G') then rnorm1 = sdot (n, resid, 1, workd(ipj), 1) rnorm1 = sqrt(abs(rnorm1)) else if (bmat .eq. 'I') then rnorm1 = snrm2(n, resid, 1) end if c if (msglvl .gt. 0 .and. iter .gt. 0) then call ivout (logfil, 1, [j], ndigit, & '_naitr: Iterative refinement for Arnoldi residual') if (msglvl .gt. 2) then xtemp(1) = rnorm xtemp(2) = rnorm1 call svout (logfil, 2, xtemp, ndigit, & '_naitr: iterative refinement ; rnorm and rnorm1 are') end if end if c c %-----------------------------------------% c | Determine if we need to perform another | c | step of re-orthogonalization. | c %-----------------------------------------% c if (rnorm1 .gt. 0.717*rnorm) then c c %---------------------------------------% c | No need for further refinement. | c | The cosine of the angle between the | c | corrected residual vector and the old | c | residual vector is greater than 0.717 | c | In other words the corrected residual | c | and the old residual vector share an | c | angle of less than arcCOS(0.717) | c %---------------------------------------% c rnorm = rnorm1 c else c c %-------------------------------------------% c | Another step of iterative refinement step | c | is required. NITREF is used by stat.h | c %-------------------------------------------% c nitref = nitref + 1 rnorm = rnorm1 iter = iter + 1 if (iter .le. 1) go to 80 c c %-------------------------------------------------% c | Otherwise RESID is numerically in the span of V | c %-------------------------------------------------% c do 95 jj = 1, n resid(jj) = zero 95 continue rnorm = zero end if c c %----------------------------------------------% c | Branch here directly if iterative refinement | c | wasn't necessary or after at most NITER_REF | c | steps of iterative refinement. | c %----------------------------------------------% c 100 continue c rstart = .false. orth2 = .false. c call arscnd (t5) titref = titref + (t5 - t4) c c %------------------------------------% c | STEP 6: Update j = j+1; Continue | c %------------------------------------% c j = j + 1 if (j .gt. k+np) then call arscnd (t1) tnaitr = tnaitr + (t1 - t0) ido = 99 do 110 i = max(1,k), k+np-1 c c %--------------------------------------------% c | Check for splitting and deflation. | c | Use a standard test as in the QR algorithm | c | REFERENCE: LAPACK subroutine slahqr | c %--------------------------------------------% c tst1 = abs( h( i, i ) ) + abs( h( i+1, i+1 ) ) if( tst1.eq.zero ) & tst1 = slanhs( '1', k+np, h, ldh, workd(n+1) ) if( abs( h( i+1,i ) ).le.max( ulp*tst1, smlnum ) ) & h(i+1,i) = zero 110 continue c if (msglvl .gt. 2) then call smout (logfil, k+np, k+np, h, ldh, ndigit, & '_naitr: Final upper Hessenberg matrix H of order K+NP') end if c go to 9000 end if c c %--------------------------------------------------------% c | Loop back to extend the factorization by another step. | c %--------------------------------------------------------% c go to 1000 c c %---------------------------------------------------------------% c | | c | E N D O F M A I N I T E R A T I O N L O O P | c | | c %---------------------------------------------------------------% c 9000 continue return c c %---------------% c | End of snaitr | c %---------------% c end