SUBROUTINE ZGELSS( M, N, NRHS, A, LDA, B, LDB, S, RCOND, RANK,
$ WORK, LWORK, RWORK, INFO )
*
* -- LAPACK driver routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
INTEGER INFO, LDA, LDB, LWORK, M, N, NRHS, RANK
DOUBLE PRECISION RCOND
* ..
* .. Array Arguments ..
DOUBLE PRECISION RWORK( * ), S( * )
COMPLEX*16 A( LDA, * ), B( LDB, * ), WORK( * )
* ..
*
* Purpose
* =======
*
* ZGELSS computes the minimum norm solution to a complex linear
* least squares problem:
*
* Minimize 2-norm(| b - A*x |).
*
* using the singular value decomposition (SVD) of A. A is an M-by-N
* matrix which may be rank-deficient.
*
* Several right hand side vectors b and solution vectors x can be
* handled in a single call; they are stored as the columns of the
* M-by-NRHS right hand side matrix B and the N-by-NRHS solution matrix
* X.
*
* The effective rank of A is determined by treating as zero those
* singular values which are less than RCOND times the largest singular
* value.
*
* Arguments
* =========
*
* M (input) INTEGER
* The number of rows of the matrix A. M >= 0.
*
* N (input) INTEGER
* The number of columns of the matrix A. N >= 0.
*
* NRHS (input) INTEGER
* The number of right hand sides, i.e., the number of columns
* of the matrices B and X. NRHS >= 0.
*
* A (input/output) COMPLEX*16 array, dimension (LDA,N)
* On entry, the M-by-N matrix A.
* On exit, the first min(m,n) rows of A are overwritten with
* its right singular vectors, stored rowwise.
*
* LDA (input) INTEGER
* The leading dimension of the array A. LDA >= max(1,M).
*
* B (input/output) COMPLEX*16 array, dimension (LDB,NRHS)
* On entry, the M-by-NRHS right hand side matrix B.
* On exit, B is overwritten by the N-by-NRHS solution matrix X.
* If m >= n and RANK = n, the residual sum-of-squares for
* the solution in the i-th column is given by the sum of
* squares of the modulus of elements n+1:m in that column.
*
* LDB (input) INTEGER
* The leading dimension of the array B. LDB >= max(1,M,N).
*
* S (output) DOUBLE PRECISION array, dimension (min(M,N))
* The singular values of A in decreasing order.
* The condition number of A in the 2-norm = S(1)/S(min(m,n)).
*
* RCOND (input) DOUBLE PRECISION
* RCOND is used to determine the effective rank of A.
* Singular values S(i) <= RCOND*S(1) are treated as zero.
* If RCOND < 0, machine precision is used instead.
*
* RANK (output) INTEGER
* The effective rank of A, i.e., the number of singular values
* which are greater than RCOND*S(1).
*
* WORK (workspace/output) COMPLEX*16 array, dimension (MAX(1,LWORK))
* On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*
* LWORK (input) INTEGER
* The dimension of the array WORK. LWORK >= 1, and also:
* LWORK >= 2*min(M,N) + max(M,N,NRHS)
* For good performance, LWORK should generally be larger.
*
* If LWORK = -1, then a workspace query is assumed; the routine
* only calculates the optimal size of the WORK array, returns
* this value as the first entry of the WORK array, and no error
* message related to LWORK is issued by XERBLA.
*
* RWORK (workspace) DOUBLE PRECISION array, dimension (5*min(M,N))
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value.
* > 0: the algorithm for computing the SVD failed to converge;
* if INFO = i, i off-diagonal elements of an intermediate
* bidiagonal form did not converge to zero.
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ZERO, ONE
PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
COMPLEX*16 CZERO, CONE
PARAMETER ( CZERO = ( 0.0D+0, 0.0D+0 ),
$ CONE = ( 1.0D+0, 0.0D+0 ) )
* ..
* .. Local Scalars ..
LOGICAL LQUERY
INTEGER BL, CHUNK, I, IASCL, IBSCL, IE, IL, IRWORK,
$ ITAU, ITAUP, ITAUQ, IWORK, LDWORK, MAXMN,
$ MAXWRK, MINMN, MINWRK, MM, MNTHR
DOUBLE PRECISION ANRM, BIGNUM, BNRM, EPS, SFMIN, SMLNUM, THR
* ..
* .. Local Arrays ..
COMPLEX*16 VDUM( 1 )
* ..
* .. External Subroutines ..
EXTERNAL DLABAD, DLASCL, DLASET, XERBLA, ZBDSQR, ZCOPY,
$ ZDRSCL, ZGEBRD, ZGELQF, ZGEMM, ZGEMV, ZGEQRF,
$ ZLACPY, ZLASCL, ZLASET, ZUNGBR, ZUNMBR, ZUNMLQ,
$ ZUNMQR
* ..
* .. External Functions ..
INTEGER ILAENV
DOUBLE PRECISION DLAMCH, ZLANGE
EXTERNAL ILAENV, DLAMCH, ZLANGE
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, MIN
* ..
* .. Executable Statements ..
*
* Test the input arguments
*
INFO = 0
MINMN = MIN( M, N )
MAXMN = MAX( M, N )
LQUERY = ( LWORK.EQ.-1 )
IF( M.LT.0 ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( NRHS.LT.0 ) THEN
INFO = -3
ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
INFO = -5
ELSE IF( LDB.LT.MAX( 1, MAXMN ) ) THEN
INFO = -7
END IF
*
* Compute workspace
* (Note: Comments in the code beginning "Workspace:" describe the
* minimal amount of workspace needed at that point in the code,
* as well as the preferred amount for good performance.
* CWorkspace refers to complex workspace, and RWorkspace refers
* to real workspace. NB refers to the optimal block size for the
* immediately following subroutine, as returned by ILAENV.)
*
IF( INFO.EQ.0 ) THEN
MINWRK = 1
MAXWRK = 1
IF( MINMN.GT.0 ) THEN
MM = M
MNTHR = ILAENV( 6, 'ZGELSS', ' ', M, N, NRHS, -1 )
IF( M.GE.N .AND. M.GE.MNTHR ) THEN
*
* Path 1a - overdetermined, with many more rows than
* columns
*
MM = N
MAXWRK = MAX( MAXWRK, N + N*ILAENV( 1, 'ZGEQRF', ' ', M,
$ N, -1, -1 ) )
MAXWRK = MAX( MAXWRK, N + NRHS*ILAENV( 1, 'ZUNMQR', 'LC',
$ M, NRHS, N, -1 ) )
END IF
IF( M.GE.N ) THEN
*
* Path 1 - overdetermined or exactly determined
*
MAXWRK = MAX( MAXWRK, 2*N + ( MM + N )*ILAENV( 1,
$ 'ZGEBRD', ' ', MM, N, -1, -1 ) )
MAXWRK = MAX( MAXWRK, 2*N + NRHS*ILAENV( 1, 'ZUNMBR',
$ 'QLC', MM, NRHS, N, -1 ) )
MAXWRK = MAX( MAXWRK, 2*N + ( N - 1 )*ILAENV( 1,
$ 'ZUNGBR', 'P', N, N, N, -1 ) )
MAXWRK = MAX( MAXWRK, N*NRHS )
MINWRK = 2*N + MAX( NRHS, M )
END IF
IF( N.GT.M ) THEN
MINWRK = 2*M + MAX( NRHS, N )
IF( N.GE.MNTHR ) THEN
*
* Path 2a - underdetermined, with many more columns
* than rows
*
MAXWRK = M + M*ILAENV( 1, 'ZGELQF', ' ', M, N, -1,
$ -1 )
MAXWRK = MAX( MAXWRK, 3*M + M*M + 2*M*ILAENV( 1,
$ 'ZGEBRD', ' ', M, M, -1, -1 ) )
MAXWRK = MAX( MAXWRK, 3*M + M*M + NRHS*ILAENV( 1,
$ 'ZUNMBR', 'QLC', M, NRHS, M, -1 ) )
MAXWRK = MAX( MAXWRK, 3*M + M*M + ( M - 1 )*ILAENV( 1,
$ 'ZUNGBR', 'P', M, M, M, -1 ) )
IF( NRHS.GT.1 ) THEN
MAXWRK = MAX( MAXWRK, M*M + M + M*NRHS )
ELSE
MAXWRK = MAX( MAXWRK, M*M + 2*M )
END IF
MAXWRK = MAX( MAXWRK, M + NRHS*ILAENV( 1, 'ZUNMLQ',
$ 'LC', N, NRHS, M, -1 ) )
ELSE
*
* Path 2 - underdetermined
*
MAXWRK = 2*M + ( N + M )*ILAENV( 1, 'ZGEBRD', ' ', M,
$ N, -1, -1 )
MAXWRK = MAX( MAXWRK, 2*M + NRHS*ILAENV( 1, 'ZUNMBR',
$ 'QLC', M, NRHS, M, -1 ) )
MAXWRK = MAX( MAXWRK, 2*M + M*ILAENV( 1, 'ZUNGBR',
$ 'P', M, N, M, -1 ) )
MAXWRK = MAX( MAXWRK, N*NRHS )
END IF
END IF
MAXWRK = MAX( MINWRK, MAXWRK )
END IF
WORK( 1 ) = MAXWRK
*
IF( LWORK.LT.MINWRK .AND. .NOT.LQUERY )
$ INFO = -12
END IF
*
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'ZGELSS', -INFO )
RETURN
ELSE IF( LQUERY ) THEN
RETURN
END IF
*
* Quick return if possible
*
IF( M.EQ.0 .OR. N.EQ.0 ) THEN
RANK = 0
RETURN
END IF
*
* Get machine parameters
*
EPS = DLAMCH( 'P' )
SFMIN = DLAMCH( 'S' )
SMLNUM = SFMIN / EPS
BIGNUM = ONE / SMLNUM
CALL DLABAD( SMLNUM, BIGNUM )
*
* Scale A if max element outside range [SMLNUM,BIGNUM]
*
ANRM = ZLANGE( 'M', M, N, A, LDA, RWORK )
IASCL = 0
IF( ANRM.GT.ZERO .AND. ANRM.LT.SMLNUM ) THEN
*
* Scale matrix norm up to SMLNUM
*
CALL ZLASCL( 'G', 0, 0, ANRM, SMLNUM, M, N, A, LDA, INFO )
IASCL = 1
ELSE IF( ANRM.GT.BIGNUM ) THEN
*
* Scale matrix norm down to BIGNUM
*
CALL ZLASCL( 'G', 0, 0, ANRM, BIGNUM, M, N, A, LDA, INFO )
IASCL = 2
ELSE IF( ANRM.EQ.ZERO ) THEN
*
* Matrix all zero. Return zero solution.
*
CALL ZLASET( 'F', MAX( M, N ), NRHS, CZERO, CZERO, B, LDB )
CALL DLASET( 'F', MINMN, 1, ZERO, ZERO, S, MINMN )
RANK = 0
GO TO 70
END IF
*
* Scale B if max element outside range [SMLNUM,BIGNUM]
*
BNRM = ZLANGE( 'M', M, NRHS, B, LDB, RWORK )
IBSCL = 0
IF( BNRM.GT.ZERO .AND. BNRM.LT.SMLNUM ) THEN
*
* Scale matrix norm up to SMLNUM
*
CALL ZLASCL( 'G', 0, 0, BNRM, SMLNUM, M, NRHS, B, LDB, INFO )
IBSCL = 1
ELSE IF( BNRM.GT.BIGNUM ) THEN
*
* Scale matrix norm down to BIGNUM
*
CALL ZLASCL( 'G', 0, 0, BNRM, BIGNUM, M, NRHS, B, LDB, INFO )
IBSCL = 2
END IF
*
* Overdetermined case
*
IF( M.GE.N ) THEN
*
* Path 1 - overdetermined or exactly determined
*
MM = M
IF( M.GE.MNTHR ) THEN
*
* Path 1a - overdetermined, with many more rows than columns
*
MM = N
ITAU = 1
IWORK = ITAU + N
*
* Compute A=Q*R
* (CWorkspace: need 2*N, prefer N+N*NB)
* (RWorkspace: none)
*
CALL ZGEQRF( M, N, A, LDA, WORK( ITAU ), WORK( IWORK ),
$ LWORK-IWORK+1, INFO )
*
* Multiply B by transpose(Q)
* (CWorkspace: need N+NRHS, prefer N+NRHS*NB)
* (RWorkspace: none)
*
CALL ZUNMQR( 'L', 'C', M, NRHS, N, A, LDA, WORK( ITAU ), B,
$ LDB, WORK( IWORK ), LWORK-IWORK+1, INFO )
*
* Zero out below R
*
IF( N.GT.1 )
$ CALL ZLASET( 'L', N-1, N-1, CZERO, CZERO, A( 2, 1 ),
$ LDA )
END IF
*
IE = 1
ITAUQ = 1
ITAUP = ITAUQ + N
IWORK = ITAUP + N
*
* Bidiagonalize R in A
* (CWorkspace: need 2*N+MM, prefer 2*N+(MM+N)*NB)
* (RWorkspace: need N)
*
CALL ZGEBRD( MM, N, A, LDA, S, RWORK( IE ), WORK( ITAUQ ),
$ WORK( ITAUP ), WORK( IWORK ), LWORK-IWORK+1,
$ INFO )
*
* Multiply B by transpose of left bidiagonalizing vectors of R
* (CWorkspace: need 2*N+NRHS, prefer 2*N+NRHS*NB)
* (RWorkspace: none)
*
CALL ZUNMBR( 'Q', 'L', 'C', MM, NRHS, N, A, LDA, WORK( ITAUQ ),
$ B, LDB, WORK( IWORK ), LWORK-IWORK+1, INFO )
*
* Generate right bidiagonalizing vectors of R in A
* (CWorkspace: need 3*N-1, prefer 2*N+(N-1)*NB)
* (RWorkspace: none)
*
CALL ZUNGBR( 'P', N, N, N, A, LDA, WORK( ITAUP ),
$ WORK( IWORK ), LWORK-IWORK+1, INFO )
IRWORK = IE + N
*
* Perform bidiagonal QR iteration
* multiply B by transpose of left singular vectors
* compute right singular vectors in A
* (CWorkspace: none)
* (RWorkspace: need BDSPAC)
*
CALL ZBDSQR( 'U', N, N, 0, NRHS, S, RWORK( IE ), A, LDA, VDUM,
$ 1, B, LDB, RWORK( IRWORK ), INFO )
IF( INFO.NE.0 )
$ GO TO 70
*
* Multiply B by reciprocals of singular values
*
THR = MAX( RCOND*S( 1 ), SFMIN )
IF( RCOND.LT.ZERO )
$ THR = MAX( EPS*S( 1 ), SFMIN )
RANK = 0
DO 10 I = 1, N
IF( S( I ).GT.THR ) THEN
CALL ZDRSCL( NRHS, S( I ), B( I, 1 ), LDB )
RANK = RANK + 1
ELSE
CALL ZLASET( 'F', 1, NRHS, CZERO, CZERO, B( I, 1 ), LDB )
END IF
10 CONTINUE
*
* Multiply B by right singular vectors
* (CWorkspace: need N, prefer N*NRHS)
* (RWorkspace: none)
*
IF( LWORK.GE.LDB*NRHS .AND. NRHS.GT.1 ) THEN
CALL ZGEMM( 'C', 'N', N, NRHS, N, CONE, A, LDA, B, LDB,
$ CZERO, WORK, LDB )
CALL ZLACPY( 'G', N, NRHS, WORK, LDB, B, LDB )
ELSE IF( NRHS.GT.1 ) THEN
CHUNK = LWORK / N
DO 20 I = 1, NRHS, CHUNK
BL = MIN( NRHS-I+1, CHUNK )
CALL ZGEMM( 'C', 'N', N, BL, N, CONE, A, LDA, B( 1, I ),
$ LDB, CZERO, WORK, N )
CALL ZLACPY( 'G', N, BL, WORK, N, B( 1, I ), LDB )
20 CONTINUE
ELSE
CALL ZGEMV( 'C', N, N, CONE, A, LDA, B, 1, CZERO, WORK, 1 )
CALL ZCOPY( N, WORK, 1, B, 1 )
END IF
*
ELSE IF( N.GE.MNTHR .AND. LWORK.GE.3*M+M*M+MAX( M, NRHS, N-2*M ) )
$ THEN
*
* Underdetermined case, M much less than N
*
* Path 2a - underdetermined, with many more columns than rows
* and sufficient workspace for an efficient algorithm
*
LDWORK = M
IF( LWORK.GE.3*M+M*LDA+MAX( M, NRHS, N-2*M ) )
$ LDWORK = LDA
ITAU = 1
IWORK = M + 1
*
* Compute A=L*Q
* (CWorkspace: need 2*M, prefer M+M*NB)
* (RWorkspace: none)
*
CALL ZGELQF( M, N, A, LDA, WORK( ITAU ), WORK( IWORK ),
$ LWORK-IWORK+1, INFO )
IL = IWORK
*
* Copy L to WORK(IL), zeroing out above it
*
CALL ZLACPY( 'L', M, M, A, LDA, WORK( IL ), LDWORK )
CALL ZLASET( 'U', M-1, M-1, CZERO, CZERO, WORK( IL+LDWORK ),
$ LDWORK )
IE = 1
ITAUQ = IL + LDWORK*M
ITAUP = ITAUQ + M
IWORK = ITAUP + M
*
* Bidiagonalize L in WORK(IL)
* (CWorkspace: need M*M+4*M, prefer M*M+3*M+2*M*NB)
* (RWorkspace: need M)
*
CALL ZGEBRD( M, M, WORK( IL ), LDWORK, S, RWORK( IE ),
$ WORK( ITAUQ ), WORK( ITAUP ), WORK( IWORK ),
$ LWORK-IWORK+1, INFO )
*
* Multiply B by transpose of left bidiagonalizing vectors of L
* (CWorkspace: need M*M+3*M+NRHS, prefer M*M+3*M+NRHS*NB)
* (RWorkspace: none)
*
CALL ZUNMBR( 'Q', 'L', 'C', M, NRHS, M, WORK( IL ), LDWORK,
$ WORK( ITAUQ ), B, LDB, WORK( IWORK ),
$ LWORK-IWORK+1, INFO )
*
* Generate right bidiagonalizing vectors of R in WORK(IL)
* (CWorkspace: need M*M+4*M-1, prefer M*M+3*M+(M-1)*NB)
* (RWorkspace: none)
*
CALL ZUNGBR( 'P', M, M, M, WORK( IL ), LDWORK, WORK( ITAUP ),
$ WORK( IWORK ), LWORK-IWORK+1, INFO )
IRWORK = IE + M
*
* Perform bidiagonal QR iteration, computing right singular
* vectors of L in WORK(IL) and multiplying B by transpose of
* left singular vectors
* (CWorkspace: need M*M)
* (RWorkspace: need BDSPAC)
*
CALL ZBDSQR( 'U', M, M, 0, NRHS, S, RWORK( IE ), WORK( IL ),
$ LDWORK, A, LDA, B, LDB, RWORK( IRWORK ), INFO )
IF( INFO.NE.0 )
$ GO TO 70
*
* Multiply B by reciprocals of singular values
*
THR = MAX( RCOND*S( 1 ), SFMIN )
IF( RCOND.LT.ZERO )
$ THR = MAX( EPS*S( 1 ), SFMIN )
RANK = 0
DO 30 I = 1, M
IF( S( I ).GT.THR ) THEN
CALL ZDRSCL( NRHS, S( I ), B( I, 1 ), LDB )
RANK = RANK + 1
ELSE
CALL ZLASET( 'F', 1, NRHS, CZERO, CZERO, B( I, 1 ), LDB )
END IF
30 CONTINUE
IWORK = IL + M*LDWORK
*
* Multiply B by right singular vectors of L in WORK(IL)
* (CWorkspace: need M*M+2*M, prefer M*M+M+M*NRHS)
* (RWorkspace: none)
*
IF( LWORK.GE.LDB*NRHS+IWORK-1 .AND. NRHS.GT.1 ) THEN
CALL ZGEMM( 'C', 'N', M, NRHS, M, CONE, WORK( IL ), LDWORK,
$ B, LDB, CZERO, WORK( IWORK ), LDB )
CALL ZLACPY( 'G', M, NRHS, WORK( IWORK ), LDB, B, LDB )
ELSE IF( NRHS.GT.1 ) THEN
CHUNK = ( LWORK-IWORK+1 ) / M
DO 40 I = 1, NRHS, CHUNK
BL = MIN( NRHS-I+1, CHUNK )
CALL ZGEMM( 'C', 'N', M, BL, M, CONE, WORK( IL ), LDWORK,
$ B( 1, I ), LDB, CZERO, WORK( IWORK ), M )
CALL ZLACPY( 'G', M, BL, WORK( IWORK ), M, B( 1, I ),
$ LDB )
40 CONTINUE
ELSE
CALL ZGEMV( 'C', M, M, CONE, WORK( IL ), LDWORK, B( 1, 1 ),
$ 1, CZERO, WORK( IWORK ), 1 )
CALL ZCOPY( M, WORK( IWORK ), 1, B( 1, 1 ), 1 )
END IF
*
* Zero out below first M rows of B
*
CALL ZLASET( 'F', N-M, NRHS, CZERO, CZERO, B( M+1, 1 ), LDB )
IWORK = ITAU + M
*
* Multiply transpose(Q) by B
* (CWorkspace: need M+NRHS, prefer M+NHRS*NB)
* (RWorkspace: none)
*
CALL ZUNMLQ( 'L', 'C', N, NRHS, M, A, LDA, WORK( ITAU ), B,
$ LDB, WORK( IWORK ), LWORK-IWORK+1, INFO )
*
ELSE
*
* Path 2 - remaining underdetermined cases
*
IE = 1
ITAUQ = 1
ITAUP = ITAUQ + M
IWORK = ITAUP + M
*
* Bidiagonalize A
* (CWorkspace: need 3*M, prefer 2*M+(M+N)*NB)
* (RWorkspace: need N)
*
CALL ZGEBRD( M, N, A, LDA, S, RWORK( IE ), WORK( ITAUQ ),
$ WORK( ITAUP ), WORK( IWORK ), LWORK-IWORK+1,
$ INFO )
*
* Multiply B by transpose of left bidiagonalizing vectors
* (CWorkspace: need 2*M+NRHS, prefer 2*M+NRHS*NB)
* (RWorkspace: none)
*
CALL ZUNMBR( 'Q', 'L', 'C', M, NRHS, N, A, LDA, WORK( ITAUQ ),
$ B, LDB, WORK( IWORK ), LWORK-IWORK+1, INFO )
*
* Generate right bidiagonalizing vectors in A
* (CWorkspace: need 3*M, prefer 2*M+M*NB)
* (RWorkspace: none)
*
CALL ZUNGBR( 'P', M, N, M, A, LDA, WORK( ITAUP ),
$ WORK( IWORK ), LWORK-IWORK+1, INFO )
IRWORK = IE + M
*
* Perform bidiagonal QR iteration,
* computing right singular vectors of A in A and
* multiplying B by transpose of left singular vectors
* (CWorkspace: none)
* (RWorkspace: need BDSPAC)
*
CALL ZBDSQR( 'L', M, N, 0, NRHS, S, RWORK( IE ), A, LDA, VDUM,
$ 1, B, LDB, RWORK( IRWORK ), INFO )
IF( INFO.NE.0 )
$ GO TO 70
*
* Multiply B by reciprocals of singular values
*
THR = MAX( RCOND*S( 1 ), SFMIN )
IF( RCOND.LT.ZERO )
$ THR = MAX( EPS*S( 1 ), SFMIN )
RANK = 0
DO 50 I = 1, M
IF( S( I ).GT.THR ) THEN
CALL ZDRSCL( NRHS, S( I ), B( I, 1 ), LDB )
RANK = RANK + 1
ELSE
CALL ZLASET( 'F', 1, NRHS, CZERO, CZERO, B( I, 1 ), LDB )
END IF
50 CONTINUE
*
* Multiply B by right singular vectors of A
* (CWorkspace: need N, prefer N*NRHS)
* (RWorkspace: none)
*
IF( LWORK.GE.LDB*NRHS .AND. NRHS.GT.1 ) THEN
CALL ZGEMM( 'C', 'N', N, NRHS, M, CONE, A, LDA, B, LDB,
$ CZERO, WORK, LDB )
CALL ZLACPY( 'G', N, NRHS, WORK, LDB, B, LDB )
ELSE IF( NRHS.GT.1 ) THEN
CHUNK = LWORK / N
DO 60 I = 1, NRHS, CHUNK
BL = MIN( NRHS-I+1, CHUNK )
CALL ZGEMM( 'C', 'N', N, BL, M, CONE, A, LDA, B( 1, I ),
$ LDB, CZERO, WORK, N )
CALL ZLACPY( 'F', N, BL, WORK, N, B( 1, I ), LDB )
60 CONTINUE
ELSE
CALL ZGEMV( 'C', M, N, CONE, A, LDA, B, 1, CZERO, WORK, 1 )
CALL ZCOPY( N, WORK, 1, B, 1 )
END IF
END IF
*
* Undo scaling
*
IF( IASCL.EQ.1 ) THEN
CALL ZLASCL( 'G', 0, 0, ANRM, SMLNUM, N, NRHS, B, LDB, INFO )
CALL DLASCL( 'G', 0, 0, SMLNUM, ANRM, MINMN, 1, S, MINMN,
$ INFO )
ELSE IF( IASCL.EQ.2 ) THEN
CALL ZLASCL( 'G', 0, 0, ANRM, BIGNUM, N, NRHS, B, LDB, INFO )
CALL DLASCL( 'G', 0, 0, BIGNUM, ANRM, MINMN, 1, S, MINMN,
$ INFO )
END IF
IF( IBSCL.EQ.1 ) THEN
CALL ZLASCL( 'G', 0, 0, SMLNUM, BNRM, N, NRHS, B, LDB, INFO )
ELSE IF( IBSCL.EQ.2 ) THEN
CALL ZLASCL( 'G', 0, 0, BIGNUM, BNRM, N, NRHS, B, LDB, INFO )
END IF
70 CONTINUE
WORK( 1 ) = MAXWRK
RETURN
*
* End of ZGELSS
*
END