c----------------------------------------------------------------------- c\BeginDoc c c\Name: pdsaitr c c Message Passing Layer: BLACS c c\Description: c Reverse communication interface for applying NP additional steps to c a K step symmetric 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 pdsaupd. The B-norm of r_{k+p} is also c computed and returned. c c\Usage: c call pdsaitr c ( COMM, IDO, BMAT, N, K, NP, MODE, RESID, RNORM, V, LDV, H, LDH, c IPNTR, WORKD, WORKL, INFO ) c c\Arguments c COMM BLACS Communicator for the processor grid. (INPUT) c 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 does not need to be c recomputed in forming OP * Q. c c BMAT Character*1. (INPUT) c BMAT specifies the type of matrix B that defines the c semi-inner product for the operator OP. See pdsaupd. 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 order of H and the number of columns of V. c c NP Integer. (INPUT) c Number of additional Arnoldi steps to take. c c MODE Integer. (INPUT) c Signifies which form for "OP". If MODE=2 then c a reduction in the number of B matrix vector multiplies c is possible since the B-norm of OP*x is equivalent to c the inv(B)-norm of A*x. c c RESID Double precision 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 Double precision scalar. (INPUT/OUTPUT) c On INPUT the B-norm of r_{k}. c On OUTPUT the B-norm of the updated residual r_{k+p}. c c V Double precision 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 Double precision (K+NP) by 2 array. (INPUT/OUTPUT) c H is used to store the generated symmetric tridiagonal matrix c with the subdiagonal in the first column starting at H(2,1) c and the main diagonal in the second column. 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 Double precision 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 where RESID is associated c with the K step Arnoldi factorization. Used to save some c computation at the first step. c On OUTPUT, WORKD(1:N) = B*RESID where RESID is associated c with the K+NP step Arnoldi factorization. c c WORKL Double precision work space used for Gram Schmidt orthogonalization c c INFO Integer. (OUTPUT) c = 0: Normal exit. c > 0: Size of an invariant subspace of OP is found that is c less than K + NP. c c\EndDoc c c----------------------------------------------------------------------- c c\BeginLib c c\Local variables: c xxxxxx real c c\Routines called: c pdgetv0 Parallel ARPACK routine to generate the initial vector. c pivout Parallel ARPACK utility routine that prints integers. c pdmout Parallel ARPACK utility routine that prints matrices. c pdvout Parallel ARPACK utility routine that prints vectors. c pdlamch ScaLAPACK routine that determines machine constants. c dlascl LAPACK routine for careful scaling of a matrix. c dgemv Level 2 BLAS routine for matrix vector multiplication. c daxpy Level 1 BLAS that computes a vector triad. c dscal Level 1 BLAS that scales a vector. c dcopy Level 1 BLAS that copies one vector to another . c ddot Level 1 BLAS that computes the scalar product of two vectors. c pdnorm2 Parallel version of 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\Parallel Modifications c Kristi Maschhoff c c\Revision history: c Starting Point: Serial Code FILE: saitr.F SID: 2.3 c c\SCCS Information: c FILE: saitr.F SID: 1.3 DATE OF SID: 3/19/97 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 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 pdsaupd 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 alphaj <- j-th component of w_{j} c rnorm = || r_{j} || c betaj+1 = rnorm 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 pdsaitr & (comm, ido, bmat, n, k, np, mode, resid, rnorm, v, ldv, h, ldh, & ipntr, workd, workl, info) c c c %------------------------------% c | BLACS Variables and Routines | c %------------------------------% c integer comm external dgsum2d 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, mode, np Double precision & rnorm c c %-----------------% c | Array Arguments | c %-----------------% c integer ipntr(3) Double precision & h(ldh,2), resid(n), v(ldv,k+np), workd(3*n), & workl(2*ldh) c c %------------% c | Parameters | c %------------% c Double precision & one, zero parameter (one = 1.0, zero = 0.0) c c %---------------% c | Local Scalars | c %---------------% c logical first, orth1, orth2, rstart, step3, step4 integer i, ierr, ipj, irj, ivj, iter, itry, j, msglvl, infol, & jj Double precision & rnorm1, wnorm, safmin, temp1 save orth1, orth2, rstart, step3, step4, & ierr, ipj, irj, ivj, iter, itry, j, msglvl, & rnorm1, safmin, wnorm c c %-----------------------% c | Local Array Arguments | c %-----------------------% c Double precision & xtemp(2) c c %----------------------% c | External Subroutines | c %----------------------% c external daxpy, dcopy, dscal, dgemv, pdgetv0, pdvout, pdmout, & dlascl, pivout, arscnd c c %--------------------% c | External Functions | c %--------------------% c Double precision & ddot, pdnorm2, pdlamch external ddot, pdnorm2, pdlamch c c %-----------------% c | Data statements | c %-----------------% c data first / .true. / c c c %---------------------% c | Intrinsic Functions | c %---------------------% c intrinsic abs, sqrt c c %-----------------------% c | Executable Statements | c %-----------------------% c if (first) then first = .false. c c %--------------------------------% c | safmin = safe minimum is such | c | that 1/sfmin does not overflow | c %--------------------------------% c safmin = pdlamch(comm,'safmin') 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 = msaitr c c %------------------------------% c | Initial call to this routine | c %------------------------------% c info = 0 step3 = .false. step4 = .false. rstart = .false. orth1 = .false. orth2 = .false. c c %--------------------------------% c | Pointer to the current step of | c | the factorization to build | c %--------------------------------% c j = k + 1 c c %------------------------------------------% c | Pointers used for reverse communication | c | when using WORKD. | c %------------------------------------------% c 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. | 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 | pdgetv0. | 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 %--------------------------------------------------------------% c 1000 continue c if (msglvl .gt. 2) then call pivout (comm, logfil, 1, [j], ndigit, & '_saitr: generating Arnoldi vector no.') call pdvout (comm, logfil, 1, [rnorm], ndigit, & '_saitr: B-norm of the current residual =') end if c c %---------------------------------------------------------% c | Check for exact zero. Equivalent to determining whether | c | a j-step Arnoldi factorization is present. | c %---------------------------------------------------------% c 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 pivout (comm, logfil, 1, [j], ndigit, & '_saitr: ****** 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 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 pdgetv0 (comm, ido, bmat, itry, .false., n, j, v, ldv, & resid, rnorm, ipntr, workd, workl, 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) tsaitr = tsaitr + (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 dcopy (n, resid, 1, v(1,j), 1) if (rnorm .ge. safmin) then temp1 = one / rnorm call dscal (n, temp1, v(1,j), 1) call dscal (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 dlascl ('General', i, i, rnorm, one, n, 1, & v(1,j), n, infol) call dlascl ('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 dcopy (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 %-----------------------------------% c call arscnd (t3) tmvopx = tmvopx + (t3 - t2) c step3 = .false. c c %------------------------------------------% c | Put another copy of OP*v_{j} into RESID. | c %------------------------------------------% c call dcopy (n, workd(irj), 1, resid, 1) c c %-------------------------------------------% c | STEP 4: Finish extending the symmetric | c | Arnoldi to length j. If MODE = 2 | c | then B*OP = B*inv(B)*A = A and | c | we don't need to compute B*OP. | c | NOTE: If MODE = 2 WORKD(IVJ:IVJ+N-1) is | c | assumed to have A*v_{j}. | c %-------------------------------------------% c if (mode .eq. 2) go to 65 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 dcopy(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 %-----------------------------------% 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 65 continue if (mode .eq. 2) then c c %----------------------------------% c | Note that the B-norm of OP*v_{j} | c | is the inv(B)-norm of A*v_{j}. | c %----------------------------------% c wnorm = ddot (n, resid, 1, workd(ivj), 1) call dgsum2d( comm, 'All', ' ', 1, 1, wnorm, 1, -1, -1 ) wnorm = sqrt(abs(wnorm)) else if (bmat .eq. 'G') then wnorm = ddot (n, resid, 1, workd(ipj), 1) call dgsum2d( comm, 'All', ' ', 1, 1, wnorm, 1, -1, -1 ) wnorm = sqrt(abs(wnorm)) else if (bmat .eq. 'I') then wnorm = pdnorm2( comm, 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 if (mode .ne. 2 ) then call dgemv('T', n, j, one, v, ldv, workd(ipj), 1, zero, & workl(1), 1) call dgsum2d( comm, 'All', ' ', j, 1, workl, j, -1, -1 ) else if (mode .eq. 2) then call dgemv('T', n, j, one, v, ldv, workd(ivj), 1, zero, & workl(1), 1) call dgsum2d( comm, 'All', ' ', j, 1, workl, j, -1, -1 ) end if c c %--------------------------------------% c | Orthgonalize r_{j} against V_{j}. | c | RESID contains OP*v_{j}. See STEP 3. | c %--------------------------------------% c call dgemv('N', n, j, -one, v, ldv, workl(1), 1, one, & resid, 1) c c %--------------------------------------% c | Extend H to have j rows and columns. | c %--------------------------------------% c h(j,2) = workl(j) if (j .eq. 1 .or. rstart) then h(j,1) = zero else h(j,1) = rnorm end if call arscnd (t4) c orth1 = .true. iter = 0 c call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 call dcopy (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 dcopy (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 = ddot (n, resid, 1, workd(ipj), 1) call dgsum2d( comm, 'All', ' ', 1, 1, rnorm, 1, -1, -1 ) rnorm = sqrt(abs(rnorm)) else if (bmat .eq. 'I') then rnorm = pdnorm2( comm, 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 %-----------------------------------------------------------% c if (rnorm .gt. 0.717*wnorm) go to 100 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 pdvout (comm, logfil, 2, xtemp, ndigit, & '_naitr: re-orthonalization ; wnorm and rnorm are') 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 dgemv ('T', n, j, one, v, ldv, workd(ipj), 1, & zero, workl, 1) call dgsum2d( comm, 'All', ' ', j, 1, workl, j, -1, -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, but only | c | H(j,j) is updated. | c %----------------------------------------------% c call dgemv ('N', n, j, -one, v, ldv, workl(1), 1, & one, resid, 1) c if (j .eq. 1 .or. rstart) h(j,1) = zero h(j,2) = h(j,2) + workl(j) c orth2 = .true. call arscnd (t2) if (bmat .eq. 'G') then nbx = nbx + 1 call dcopy (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 dcopy (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 = ddot (n, resid, 1, workd(ipj), 1) call dgsum2d( comm, 'All', ' ', 1, 1, rnorm1, 1, -1, -1 ) rnorm1 = sqrt(abs(rnorm1)) else if (bmat .eq. 'I') then rnorm1 = pdnorm2( comm, n, resid, 1 ) end if c if (msglvl .gt. 0 .and. iter .gt. 0) then call pivout (comm, logfil, 1, [j], ndigit, & '_naitr: Iterative refinement for Arnoldi residual') if (msglvl .gt. 2) then xtemp(1) = rnorm xtemp(2) = rnorm1 call pdvout (comm, 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 %--------------------------------% 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 | Make sure the last off-diagonal element is non negative | c | If not perform a similarity transformation on H(1:j,1:j) | c | and scale v(:,j) by -1. | c %----------------------------------------------------------% c if (h(j,1) .lt. zero) then h(j,1) = -h(j,1) if ( j .lt. k+np) then call dscal(n, -one, v(1,j+1), 1) else call dscal(n, -one, resid, 1) end if end if c c %------------------------------------% c | STEP 6: Update j = j+1; Continue | c %------------------------------------% c j = j + 1 if (j .gt. k+np) then call arscnd (t1) tsaitr = tsaitr + (t1 - t0) ido = 99 c if (msglvl .gt. 1) then call pdvout (comm, logfil, k+np, h(1,2), ndigit, & '_saitr: main diagonal of matrix H of step K+NP.') if (k+np .gt. 1) then call pdvout (comm, logfil, k+np-1, h(2,1), ndigit, & '_saitr: sub diagonal of matrix H of step K+NP.') end if 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 pdsaitr | c %----------------% c end