743 lines
23 KiB
FortranFixed
743 lines
23 KiB
FortranFixed
SUBROUTINE DBDSQR( UPLO, N, NCVT, NRU, NCC, D, E, VT, LDVT, U,
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$ LDU, C, LDC, WORK, INFO )
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*
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* -- LAPACK routine (version 3.1.1) --
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* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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* January 2007
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*
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* .. Scalar Arguments ..
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CHARACTER UPLO
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INTEGER INFO, LDC, LDU, LDVT, N, NCC, NCVT, NRU
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION C( LDC, * ), D( * ), E( * ), U( LDU, * ),
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$ VT( LDVT, * ), WORK( * )
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* ..
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*
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* Purpose
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* =======
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*
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* DBDSQR computes the singular values and, optionally, the right and/or
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* left singular vectors from the singular value decomposition (SVD) of
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* a real N-by-N (upper or lower) bidiagonal matrix B using the implicit
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* zero-shift QR algorithm. The SVD of B has the form
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*
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* B = Q * S * P**T
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*
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* where S is the diagonal matrix of singular values, Q is an orthogonal
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* matrix of left singular vectors, and P is an orthogonal matrix of
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* right singular vectors. If left singular vectors are requested, this
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* subroutine actually returns U*Q instead of Q, and, if right singular
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* vectors are requested, this subroutine returns P**T*VT instead of
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* P**T, for given real input matrices U and VT. When U and VT are the
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* orthogonal matrices that reduce a general matrix A to bidiagonal
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* form: A = U*B*VT, as computed by DGEBRD, then
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*
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* A = (U*Q) * S * (P**T*VT)
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*
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* is the SVD of A. Optionally, the subroutine may also compute Q**T*C
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* for a given real input matrix C.
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*
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* See "Computing Small Singular Values of Bidiagonal Matrices With
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* Guaranteed High Relative Accuracy," by J. Demmel and W. Kahan,
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* LAPACK Working Note #3 (or SIAM J. Sci. Statist. Comput. vol. 11,
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* no. 5, pp. 873-912, Sept 1990) and
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* "Accurate singular values and differential qd algorithms," by
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* B. Parlett and V. Fernando, Technical Report CPAM-554, Mathematics
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* Department, University of California at Berkeley, July 1992
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* for a detailed description of the algorithm.
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*
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* Arguments
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* =========
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*
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* UPLO (input) CHARACTER*1
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* = 'U': B is upper bidiagonal;
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* = 'L': B is lower bidiagonal.
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*
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* N (input) INTEGER
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* The order of the matrix B. N >= 0.
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*
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* NCVT (input) INTEGER
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* The number of columns of the matrix VT. NCVT >= 0.
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*
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* NRU (input) INTEGER
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* The number of rows of the matrix U. NRU >= 0.
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*
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* NCC (input) INTEGER
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* The number of columns of the matrix C. NCC >= 0.
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*
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* D (input/output) DOUBLE PRECISION array, dimension (N)
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* On entry, the n diagonal elements of the bidiagonal matrix B.
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* On exit, if INFO=0, the singular values of B in decreasing
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* order.
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*
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* E (input/output) DOUBLE PRECISION array, dimension (N-1)
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* On entry, the N-1 offdiagonal elements of the bidiagonal
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* matrix B.
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* On exit, if INFO = 0, E is destroyed; if INFO > 0, D and E
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* will contain the diagonal and superdiagonal elements of a
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* bidiagonal matrix orthogonally equivalent to the one given
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* as input.
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*
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* VT (input/output) DOUBLE PRECISION array, dimension (LDVT, NCVT)
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* On entry, an N-by-NCVT matrix VT.
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* On exit, VT is overwritten by P**T * VT.
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* Not referenced if NCVT = 0.
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*
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* LDVT (input) INTEGER
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* The leading dimension of the array VT.
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* LDVT >= max(1,N) if NCVT > 0; LDVT >= 1 if NCVT = 0.
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*
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* U (input/output) DOUBLE PRECISION array, dimension (LDU, N)
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* On entry, an NRU-by-N matrix U.
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* On exit, U is overwritten by U * Q.
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* Not referenced if NRU = 0.
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*
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* LDU (input) INTEGER
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* The leading dimension of the array U. LDU >= max(1,NRU).
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*
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* C (input/output) DOUBLE PRECISION array, dimension (LDC, NCC)
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* On entry, an N-by-NCC matrix C.
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* On exit, C is overwritten by Q**T * C.
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* Not referenced if NCC = 0.
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*
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* LDC (input) INTEGER
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* The leading dimension of the array C.
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* LDC >= max(1,N) if NCC > 0; LDC >=1 if NCC = 0.
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*
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* WORK (workspace) DOUBLE PRECISION array, dimension (2*N)
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* if NCVT = NRU = NCC = 0, (max(1, 4*N)) otherwise
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*
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* INFO (output) INTEGER
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* = 0: successful exit
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* < 0: If INFO = -i, the i-th argument had an illegal value
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* > 0: the algorithm did not converge; D and E contain the
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* elements of a bidiagonal matrix which is orthogonally
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* similar to the input matrix B; if INFO = i, i
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* elements of E have not converged to zero.
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*
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* Internal Parameters
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* ===================
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*
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* TOLMUL DOUBLE PRECISION, default = max(10,min(100,EPS**(-1/8)))
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* TOLMUL controls the convergence criterion of the QR loop.
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* If it is positive, TOLMUL*EPS is the desired relative
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* precision in the computed singular values.
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* If it is negative, abs(TOLMUL*EPS*sigma_max) is the
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* desired absolute accuracy in the computed singular
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* values (corresponds to relative accuracy
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* abs(TOLMUL*EPS) in the largest singular value.
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* abs(TOLMUL) should be between 1 and 1/EPS, and preferably
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* between 10 (for fast convergence) and .1/EPS
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* (for there to be some accuracy in the results).
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* Default is to lose at either one eighth or 2 of the
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* available decimal digits in each computed singular value
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* (whichever is smaller).
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*
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* MAXITR INTEGER, default = 6
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* MAXITR controls the maximum number of passes of the
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* algorithm through its inner loop. The algorithms stops
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* (and so fails to converge) if the number of passes
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* through the inner loop exceeds MAXITR*N**2.
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D0 )
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DOUBLE PRECISION ONE
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PARAMETER ( ONE = 1.0D0 )
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DOUBLE PRECISION NEGONE
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PARAMETER ( NEGONE = -1.0D0 )
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DOUBLE PRECISION HNDRTH
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PARAMETER ( HNDRTH = 0.01D0 )
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DOUBLE PRECISION TEN
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PARAMETER ( TEN = 10.0D0 )
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DOUBLE PRECISION HNDRD
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PARAMETER ( HNDRD = 100.0D0 )
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DOUBLE PRECISION MEIGTH
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PARAMETER ( MEIGTH = -0.125D0 )
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INTEGER MAXITR
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PARAMETER ( MAXITR = 6 )
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* ..
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* .. Local Scalars ..
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LOGICAL LOWER, ROTATE
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INTEGER I, IDIR, ISUB, ITER, J, LL, LLL, M, MAXIT, NM1,
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$ NM12, NM13, OLDLL, OLDM
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DOUBLE PRECISION ABSE, ABSS, COSL, COSR, CS, EPS, F, G, H, MU,
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$ OLDCS, OLDSN, R, SHIFT, SIGMN, SIGMX, SINL,
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$ SINR, SLL, SMAX, SMIN, SMINL, SMINOA,
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$ SN, THRESH, TOL, TOLMUL, UNFL
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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DOUBLE PRECISION DLAMCH
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EXTERNAL LSAME, DLAMCH
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* ..
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* .. External Subroutines ..
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EXTERNAL DLARTG, DLAS2, DLASQ1, DLASR, DLASV2, DROT,
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$ DSCAL, DSWAP, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, DBLE, MAX, MIN, SIGN, SQRT
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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INFO = 0
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LOWER = LSAME( UPLO, 'L' )
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IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LOWER ) THEN
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INFO = -1
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ELSE IF( N.LT.0 ) THEN
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INFO = -2
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ELSE IF( NCVT.LT.0 ) THEN
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INFO = -3
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ELSE IF( NRU.LT.0 ) THEN
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INFO = -4
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ELSE IF( NCC.LT.0 ) THEN
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INFO = -5
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ELSE IF( ( NCVT.EQ.0 .AND. LDVT.LT.1 ) .OR.
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$ ( NCVT.GT.0 .AND. LDVT.LT.MAX( 1, N ) ) ) THEN
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INFO = -9
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ELSE IF( LDU.LT.MAX( 1, NRU ) ) THEN
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INFO = -11
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ELSE IF( ( NCC.EQ.0 .AND. LDC.LT.1 ) .OR.
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$ ( NCC.GT.0 .AND. LDC.LT.MAX( 1, N ) ) ) THEN
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INFO = -13
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'DBDSQR', -INFO )
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RETURN
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END IF
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IF( N.EQ.0 )
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$ RETURN
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IF( N.EQ.1 )
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$ GO TO 160
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*
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* ROTATE is true if any singular vectors desired, false otherwise
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*
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ROTATE = ( NCVT.GT.0 ) .OR. ( NRU.GT.0 ) .OR. ( NCC.GT.0 )
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*
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* If no singular vectors desired, use qd algorithm
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*
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IF( .NOT.ROTATE ) THEN
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CALL DLASQ1( N, D, E, WORK, INFO )
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RETURN
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END IF
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*
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NM1 = N - 1
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NM12 = NM1 + NM1
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NM13 = NM12 + NM1
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IDIR = 0
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*
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* Get machine constants
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*
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EPS = DLAMCH( 'Epsilon' )
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UNFL = DLAMCH( 'Safe minimum' )
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*
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* If matrix lower bidiagonal, rotate to be upper bidiagonal
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* by applying Givens rotations on the left
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*
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IF( LOWER ) THEN
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DO 10 I = 1, N - 1
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CALL DLARTG( D( I ), E( I ), CS, SN, R )
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D( I ) = R
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E( I ) = SN*D( I+1 )
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D( I+1 ) = CS*D( I+1 )
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WORK( I ) = CS
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WORK( NM1+I ) = SN
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10 CONTINUE
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*
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* Update singular vectors if desired
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*
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IF( NRU.GT.0 )
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$ CALL DLASR( 'R', 'V', 'F', NRU, N, WORK( 1 ), WORK( N ), U,
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$ LDU )
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IF( NCC.GT.0 )
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$ CALL DLASR( 'L', 'V', 'F', N, NCC, WORK( 1 ), WORK( N ), C,
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$ LDC )
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END IF
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*
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* Compute singular values to relative accuracy TOL
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* (By setting TOL to be negative, algorithm will compute
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* singular values to absolute accuracy ABS(TOL)*norm(input matrix))
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*
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TOLMUL = MAX( TEN, MIN( HNDRD, EPS**MEIGTH ) )
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TOL = TOLMUL*EPS
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*
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* Compute approximate maximum, minimum singular values
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*
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SMAX = ZERO
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DO 20 I = 1, N
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SMAX = MAX( SMAX, ABS( D( I ) ) )
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20 CONTINUE
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DO 30 I = 1, N - 1
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SMAX = MAX( SMAX, ABS( E( I ) ) )
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30 CONTINUE
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SMINL = ZERO
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IF( TOL.GE.ZERO ) THEN
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*
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* Relative accuracy desired
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*
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SMINOA = ABS( D( 1 ) )
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IF( SMINOA.EQ.ZERO )
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$ GO TO 50
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MU = SMINOA
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DO 40 I = 2, N
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MU = ABS( D( I ) )*( MU / ( MU+ABS( E( I-1 ) ) ) )
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SMINOA = MIN( SMINOA, MU )
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IF( SMINOA.EQ.ZERO )
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$ GO TO 50
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40 CONTINUE
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50 CONTINUE
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SMINOA = SMINOA / SQRT( DBLE( N ) )
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THRESH = MAX( TOL*SMINOA, MAXITR*N*N*UNFL )
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ELSE
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*
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* Absolute accuracy desired
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*
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THRESH = MAX( ABS( TOL )*SMAX, MAXITR*N*N*UNFL )
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END IF
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*
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* Prepare for main iteration loop for the singular values
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* (MAXIT is the maximum number of passes through the inner
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* loop permitted before nonconvergence signalled.)
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*
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MAXIT = MAXITR*N*N
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ITER = 0
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OLDLL = -1
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OLDM = -1
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*
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* M points to last element of unconverged part of matrix
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*
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M = N
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*
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* Begin main iteration loop
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*
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60 CONTINUE
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*
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* Check for convergence or exceeding iteration count
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*
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IF( M.LE.1 )
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$ GO TO 160
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IF( ITER.GT.MAXIT )
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$ GO TO 200
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*
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* Find diagonal block of matrix to work on
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*
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IF( TOL.LT.ZERO .AND. ABS( D( M ) ).LE.THRESH )
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$ D( M ) = ZERO
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SMAX = ABS( D( M ) )
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SMIN = SMAX
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DO 70 LLL = 1, M - 1
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LL = M - LLL
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ABSS = ABS( D( LL ) )
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ABSE = ABS( E( LL ) )
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IF( TOL.LT.ZERO .AND. ABSS.LE.THRESH )
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$ D( LL ) = ZERO
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IF( ABSE.LE.THRESH )
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$ GO TO 80
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SMIN = MIN( SMIN, ABSS )
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SMAX = MAX( SMAX, ABSS, ABSE )
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70 CONTINUE
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LL = 0
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GO TO 90
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80 CONTINUE
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E( LL ) = ZERO
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*
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* Matrix splits since E(LL) = 0
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*
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IF( LL.EQ.M-1 ) THEN
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*
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* Convergence of bottom singular value, return to top of loop
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*
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M = M - 1
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GO TO 60
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END IF
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90 CONTINUE
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LL = LL + 1
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*
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* E(LL) through E(M-1) are nonzero, E(LL-1) is zero
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*
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IF( LL.EQ.M-1 ) THEN
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*
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* 2 by 2 block, handle separately
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*
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CALL DLASV2( D( M-1 ), E( M-1 ), D( M ), SIGMN, SIGMX, SINR,
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$ COSR, SINL, COSL )
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D( M-1 ) = SIGMX
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E( M-1 ) = ZERO
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D( M ) = SIGMN
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*
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* Compute singular vectors, if desired
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*
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IF( NCVT.GT.0 )
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$ CALL DROT( NCVT, VT( M-1, 1 ), LDVT, VT( M, 1 ), LDVT, COSR,
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$ SINR )
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IF( NRU.GT.0 )
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$ CALL DROT( NRU, U( 1, M-1 ), 1, U( 1, M ), 1, COSL, SINL )
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IF( NCC.GT.0 )
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$ CALL DROT( NCC, C( M-1, 1 ), LDC, C( M, 1 ), LDC, COSL,
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$ SINL )
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M = M - 2
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GO TO 60
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END IF
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*
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* If working on new submatrix, choose shift direction
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* (from larger end diagonal element towards smaller)
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*
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IF( LL.GT.OLDM .OR. M.LT.OLDLL ) THEN
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IF( ABS( D( LL ) ).GE.ABS( D( M ) ) ) THEN
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*
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* Chase bulge from top (big end) to bottom (small end)
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*
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IDIR = 1
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ELSE
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*
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* Chase bulge from bottom (big end) to top (small end)
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*
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IDIR = 2
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END IF
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END IF
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*
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* Apply convergence tests
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*
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IF( IDIR.EQ.1 ) THEN
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*
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* Run convergence test in forward direction
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* First apply standard test to bottom of matrix
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*
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IF( ABS( E( M-1 ) ).LE.ABS( TOL )*ABS( D( M ) ) .OR.
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$ ( TOL.LT.ZERO .AND. ABS( E( M-1 ) ).LE.THRESH ) ) THEN
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E( M-1 ) = ZERO
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GO TO 60
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END IF
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*
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IF( TOL.GE.ZERO ) THEN
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*
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* If relative accuracy desired,
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* apply convergence criterion forward
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*
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MU = ABS( D( LL ) )
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SMINL = MU
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DO 100 LLL = LL, M - 1
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IF( ABS( E( LLL ) ).LE.TOL*MU ) THEN
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E( LLL ) = ZERO
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GO TO 60
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END IF
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MU = ABS( D( LLL+1 ) )*( MU / ( MU+ABS( E( LLL ) ) ) )
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SMINL = MIN( SMINL, MU )
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100 CONTINUE
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END IF
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*
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ELSE
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*
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* Run convergence test in backward direction
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* First apply standard test to top of matrix
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*
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IF( ABS( E( LL ) ).LE.ABS( TOL )*ABS( D( LL ) ) .OR.
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$ ( TOL.LT.ZERO .AND. ABS( E( LL ) ).LE.THRESH ) ) THEN
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E( LL ) = ZERO
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GO TO 60
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END IF
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*
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|
IF( TOL.GE.ZERO ) THEN
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*
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* If relative accuracy desired,
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* apply convergence criterion backward
|
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*
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MU = ABS( D( M ) )
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SMINL = MU
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DO 110 LLL = M - 1, LL, -1
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IF( ABS( E( LLL ) ).LE.TOL*MU ) THEN
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E( LLL ) = ZERO
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GO TO 60
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END IF
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MU = ABS( D( LLL ) )*( MU / ( MU+ABS( E( LLL ) ) ) )
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SMINL = MIN( SMINL, MU )
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110 CONTINUE
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END IF
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END IF
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OLDLL = LL
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OLDM = M
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*
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* Compute shift. First, test if shifting would ruin relative
|
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* accuracy, and if so set the shift to zero.
|
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*
|
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IF( TOL.GE.ZERO .AND. N*TOL*( SMINL / SMAX ).LE.
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$ MAX( EPS, HNDRTH*TOL ) ) THEN
|
|
*
|
|
* Use a zero shift to avoid loss of relative accuracy
|
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*
|
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SHIFT = ZERO
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ELSE
|
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*
|
|
* Compute the shift from 2-by-2 block at end of matrix
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*
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|
IF( IDIR.EQ.1 ) THEN
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SLL = ABS( D( LL ) )
|
|
CALL DLAS2( D( M-1 ), E( M-1 ), D( M ), SHIFT, R )
|
|
ELSE
|
|
SLL = ABS( D( M ) )
|
|
CALL DLAS2( D( LL ), E( LL ), D( LL+1 ), SHIFT, R )
|
|
END IF
|
|
*
|
|
* Test if shift negligible, and if so set to zero
|
|
*
|
|
IF( SLL.GT.ZERO ) THEN
|
|
IF( ( SHIFT / SLL )**2.LT.EPS )
|
|
$ SHIFT = ZERO
|
|
END IF
|
|
END IF
|
|
*
|
|
* Increment iteration count
|
|
*
|
|
ITER = ITER + M - LL
|
|
*
|
|
* If SHIFT = 0, do simplified QR iteration
|
|
*
|
|
IF( SHIFT.EQ.ZERO ) THEN
|
|
IF( IDIR.EQ.1 ) THEN
|
|
*
|
|
* Chase bulge from top to bottom
|
|
* Save cosines and sines for later singular vector updates
|
|
*
|
|
CS = ONE
|
|
OLDCS = ONE
|
|
DO 120 I = LL, M - 1
|
|
CALL DLARTG( D( I )*CS, E( I ), CS, SN, R )
|
|
IF( I.GT.LL )
|
|
$ E( I-1 ) = OLDSN*R
|
|
CALL DLARTG( OLDCS*R, D( I+1 )*SN, OLDCS, OLDSN, D( I ) )
|
|
WORK( I-LL+1 ) = CS
|
|
WORK( I-LL+1+NM1 ) = SN
|
|
WORK( I-LL+1+NM12 ) = OLDCS
|
|
WORK( I-LL+1+NM13 ) = OLDSN
|
|
120 CONTINUE
|
|
H = D( M )*CS
|
|
D( M ) = H*OLDCS
|
|
E( M-1 ) = H*OLDSN
|
|
*
|
|
* Update singular vectors
|
|
*
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'F', M-LL+1, NCVT, WORK( 1 ),
|
|
$ WORK( N ), VT( LL, 1 ), LDVT )
|
|
IF( NRU.GT.0 )
|
|
$ CALL DLASR( 'R', 'V', 'F', NRU, M-LL+1, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), U( 1, LL ), LDU )
|
|
IF( NCC.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'F', M-LL+1, NCC, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), C( LL, 1 ), LDC )
|
|
*
|
|
* Test convergence
|
|
*
|
|
IF( ABS( E( M-1 ) ).LE.THRESH )
|
|
$ E( M-1 ) = ZERO
|
|
*
|
|
ELSE
|
|
*
|
|
* Chase bulge from bottom to top
|
|
* Save cosines and sines for later singular vector updates
|
|
*
|
|
CS = ONE
|
|
OLDCS = ONE
|
|
DO 130 I = M, LL + 1, -1
|
|
CALL DLARTG( D( I )*CS, E( I-1 ), CS, SN, R )
|
|
IF( I.LT.M )
|
|
$ E( I ) = OLDSN*R
|
|
CALL DLARTG( OLDCS*R, D( I-1 )*SN, OLDCS, OLDSN, D( I ) )
|
|
WORK( I-LL ) = CS
|
|
WORK( I-LL+NM1 ) = -SN
|
|
WORK( I-LL+NM12 ) = OLDCS
|
|
WORK( I-LL+NM13 ) = -OLDSN
|
|
130 CONTINUE
|
|
H = D( LL )*CS
|
|
D( LL ) = H*OLDCS
|
|
E( LL ) = H*OLDSN
|
|
*
|
|
* Update singular vectors
|
|
*
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'B', M-LL+1, NCVT, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), VT( LL, 1 ), LDVT )
|
|
IF( NRU.GT.0 )
|
|
$ CALL DLASR( 'R', 'V', 'B', NRU, M-LL+1, WORK( 1 ),
|
|
$ WORK( N ), U( 1, LL ), LDU )
|
|
IF( NCC.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'B', M-LL+1, NCC, WORK( 1 ),
|
|
$ WORK( N ), C( LL, 1 ), LDC )
|
|
*
|
|
* Test convergence
|
|
*
|
|
IF( ABS( E( LL ) ).LE.THRESH )
|
|
$ E( LL ) = ZERO
|
|
END IF
|
|
ELSE
|
|
*
|
|
* Use nonzero shift
|
|
*
|
|
IF( IDIR.EQ.1 ) THEN
|
|
*
|
|
* Chase bulge from top to bottom
|
|
* Save cosines and sines for later singular vector updates
|
|
*
|
|
F = ( ABS( D( LL ) )-SHIFT )*
|
|
$ ( SIGN( ONE, D( LL ) )+SHIFT / D( LL ) )
|
|
G = E( LL )
|
|
DO 140 I = LL, M - 1
|
|
CALL DLARTG( F, G, COSR, SINR, R )
|
|
IF( I.GT.LL )
|
|
$ E( I-1 ) = R
|
|
F = COSR*D( I ) + SINR*E( I )
|
|
E( I ) = COSR*E( I ) - SINR*D( I )
|
|
G = SINR*D( I+1 )
|
|
D( I+1 ) = COSR*D( I+1 )
|
|
CALL DLARTG( F, G, COSL, SINL, R )
|
|
D( I ) = R
|
|
F = COSL*E( I ) + SINL*D( I+1 )
|
|
D( I+1 ) = COSL*D( I+1 ) - SINL*E( I )
|
|
IF( I.LT.M-1 ) THEN
|
|
G = SINL*E( I+1 )
|
|
E( I+1 ) = COSL*E( I+1 )
|
|
END IF
|
|
WORK( I-LL+1 ) = COSR
|
|
WORK( I-LL+1+NM1 ) = SINR
|
|
WORK( I-LL+1+NM12 ) = COSL
|
|
WORK( I-LL+1+NM13 ) = SINL
|
|
140 CONTINUE
|
|
E( M-1 ) = F
|
|
*
|
|
* Update singular vectors
|
|
*
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'F', M-LL+1, NCVT, WORK( 1 ),
|
|
$ WORK( N ), VT( LL, 1 ), LDVT )
|
|
IF( NRU.GT.0 )
|
|
$ CALL DLASR( 'R', 'V', 'F', NRU, M-LL+1, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), U( 1, LL ), LDU )
|
|
IF( NCC.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'F', M-LL+1, NCC, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), C( LL, 1 ), LDC )
|
|
*
|
|
* Test convergence
|
|
*
|
|
IF( ABS( E( M-1 ) ).LE.THRESH )
|
|
$ E( M-1 ) = ZERO
|
|
*
|
|
ELSE
|
|
*
|
|
* Chase bulge from bottom to top
|
|
* Save cosines and sines for later singular vector updates
|
|
*
|
|
F = ( ABS( D( M ) )-SHIFT )*( SIGN( ONE, D( M ) )+SHIFT /
|
|
$ D( M ) )
|
|
G = E( M-1 )
|
|
DO 150 I = M, LL + 1, -1
|
|
CALL DLARTG( F, G, COSR, SINR, R )
|
|
IF( I.LT.M )
|
|
$ E( I ) = R
|
|
F = COSR*D( I ) + SINR*E( I-1 )
|
|
E( I-1 ) = COSR*E( I-1 ) - SINR*D( I )
|
|
G = SINR*D( I-1 )
|
|
D( I-1 ) = COSR*D( I-1 )
|
|
CALL DLARTG( F, G, COSL, SINL, R )
|
|
D( I ) = R
|
|
F = COSL*E( I-1 ) + SINL*D( I-1 )
|
|
D( I-1 ) = COSL*D( I-1 ) - SINL*E( I-1 )
|
|
IF( I.GT.LL+1 ) THEN
|
|
G = SINL*E( I-2 )
|
|
E( I-2 ) = COSL*E( I-2 )
|
|
END IF
|
|
WORK( I-LL ) = COSR
|
|
WORK( I-LL+NM1 ) = -SINR
|
|
WORK( I-LL+NM12 ) = COSL
|
|
WORK( I-LL+NM13 ) = -SINL
|
|
150 CONTINUE
|
|
E( LL ) = F
|
|
*
|
|
* Test convergence
|
|
*
|
|
IF( ABS( E( LL ) ).LE.THRESH )
|
|
$ E( LL ) = ZERO
|
|
*
|
|
* Update singular vectors if desired
|
|
*
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'B', M-LL+1, NCVT, WORK( NM12+1 ),
|
|
$ WORK( NM13+1 ), VT( LL, 1 ), LDVT )
|
|
IF( NRU.GT.0 )
|
|
$ CALL DLASR( 'R', 'V', 'B', NRU, M-LL+1, WORK( 1 ),
|
|
$ WORK( N ), U( 1, LL ), LDU )
|
|
IF( NCC.GT.0 )
|
|
$ CALL DLASR( 'L', 'V', 'B', M-LL+1, NCC, WORK( 1 ),
|
|
$ WORK( N ), C( LL, 1 ), LDC )
|
|
END IF
|
|
END IF
|
|
*
|
|
* QR iteration finished, go back and check convergence
|
|
*
|
|
GO TO 60
|
|
*
|
|
* All singular values converged, so make them positive
|
|
*
|
|
160 CONTINUE
|
|
DO 170 I = 1, N
|
|
IF( D( I ).LT.ZERO ) THEN
|
|
D( I ) = -D( I )
|
|
*
|
|
* Change sign of singular vectors, if desired
|
|
*
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DSCAL( NCVT, NEGONE, VT( I, 1 ), LDVT )
|
|
END IF
|
|
170 CONTINUE
|
|
*
|
|
* Sort the singular values into decreasing order (insertion sort on
|
|
* singular values, but only one transposition per singular vector)
|
|
*
|
|
DO 190 I = 1, N - 1
|
|
*
|
|
* Scan for smallest D(I)
|
|
*
|
|
ISUB = 1
|
|
SMIN = D( 1 )
|
|
DO 180 J = 2, N + 1 - I
|
|
IF( D( J ).LE.SMIN ) THEN
|
|
ISUB = J
|
|
SMIN = D( J )
|
|
END IF
|
|
180 CONTINUE
|
|
IF( ISUB.NE.N+1-I ) THEN
|
|
*
|
|
* Swap singular values and vectors
|
|
*
|
|
D( ISUB ) = D( N+1-I )
|
|
D( N+1-I ) = SMIN
|
|
IF( NCVT.GT.0 )
|
|
$ CALL DSWAP( NCVT, VT( ISUB, 1 ), LDVT, VT( N+1-I, 1 ),
|
|
$ LDVT )
|
|
IF( NRU.GT.0 )
|
|
$ CALL DSWAP( NRU, U( 1, ISUB ), 1, U( 1, N+1-I ), 1 )
|
|
IF( NCC.GT.0 )
|
|
$ CALL DSWAP( NCC, C( ISUB, 1 ), LDC, C( N+1-I, 1 ), LDC )
|
|
END IF
|
|
190 CONTINUE
|
|
GO TO 220
|
|
*
|
|
* Maximum number of iterations exceeded, failure to converge
|
|
*
|
|
200 CONTINUE
|
|
INFO = 0
|
|
DO 210 I = 1, N - 1
|
|
IF( E( I ).NE.ZERO )
|
|
$ INFO = INFO + 1
|
|
210 CONTINUE
|
|
220 CONTINUE
|
|
RETURN
|
|
*
|
|
* End of DBDSQR
|
|
*
|
|
END
|