SUBROUTINE DLASD0( N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK, \$ WORK, INFO ) * * -- LAPACK auxiliary routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. INTEGER INFO, LDU, LDVT, N, SMLSIZ, SQRE * .. * .. Array Arguments .. INTEGER IWORK( * ) DOUBLE PRECISION D( * ), E( * ), U( LDU, * ), VT( LDVT, * ), \$ WORK( * ) * .. * * Purpose * ======= * * Using a divide and conquer approach, DLASD0 computes the singular * value decomposition (SVD) of a real upper bidiagonal N-by-M * matrix B with diagonal D and offdiagonal E, where M = N + SQRE. * The algorithm computes orthogonal matrices U and VT such that * B = U * S * VT. The singular values S are overwritten on D. * * A related subroutine, DLASDA, computes only the singular values, * and optionally, the singular vectors in compact form. * * Arguments * ========= * * N (input) INTEGER * On entry, the row dimension of the upper bidiagonal matrix. * This is also the dimension of the main diagonal array D. * * SQRE (input) INTEGER * Specifies the column dimension of the bidiagonal matrix. * = 0: The bidiagonal matrix has column dimension M = N; * = 1: The bidiagonal matrix has column dimension M = N+1; * * D (input/output) DOUBLE PRECISION array, dimension (N) * On entry D contains the main diagonal of the bidiagonal * matrix. * On exit D, if INFO = 0, contains its singular values. * * E (input) DOUBLE PRECISION array, dimension (M-1) * Contains the subdiagonal entries of the bidiagonal matrix. * On exit, E has been destroyed. * * U (output) DOUBLE PRECISION array, dimension at least (LDQ, N) * On exit, U contains the left singular vectors. * * LDU (input) INTEGER * On entry, leading dimension of U. * * VT (output) DOUBLE PRECISION array, dimension at least (LDVT, M) * On exit, VT' contains the right singular vectors. * * LDVT (input) INTEGER * On entry, leading dimension of VT. * * SMLSIZ (input) INTEGER * On entry, maximum size of the subproblems at the * bottom of the computation tree. * * IWORK (workspace) INTEGER work array. * Dimension must be at least (8 * N) * * WORK (workspace) DOUBLE PRECISION work array. * Dimension must be at least (3 * M**2 + 2 * M) * * INFO (output) INTEGER * = 0: successful exit. * < 0: if INFO = -i, the i-th argument had an illegal value. * > 0: if INFO = 1, an singular value did not converge * * Further Details * =============== * * Based on contributions by * Ming Gu and Huan Ren, Computer Science Division, University of * California at Berkeley, USA * * ===================================================================== * * .. Local Scalars .. INTEGER I, I1, IC, IDXQ, IDXQC, IM1, INODE, ITEMP, IWK, \$ J, LF, LL, LVL, M, NCC, ND, NDB1, NDIML, NDIMR, \$ NL, NLF, NLP1, NLVL, NR, NRF, NRP1, SQREI DOUBLE PRECISION ALPHA, BETA * .. * .. External Subroutines .. EXTERNAL DLASD1, DLASDQ, DLASDT, XERBLA * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 * IF( N.LT.0 ) THEN INFO = -1 ELSE IF( ( SQRE.LT.0 ) .OR. ( SQRE.GT.1 ) ) THEN INFO = -2 END IF * M = N + SQRE * IF( LDU.LT.N ) THEN INFO = -6 ELSE IF( LDVT.LT.M ) THEN INFO = -8 ELSE IF( SMLSIZ.LT.3 ) THEN INFO = -9 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'DLASD0', -INFO ) RETURN END IF * * If the input matrix is too small, call DLASDQ to find the SVD. * IF( N.LE.SMLSIZ ) THEN CALL DLASDQ( 'U', SQRE, N, M, N, 0, D, E, VT, LDVT, U, LDU, U, \$ LDU, WORK, INFO ) RETURN END IF * * Set up the computation tree. * INODE = 1 NDIML = INODE + N NDIMR = NDIML + N IDXQ = NDIMR + N IWK = IDXQ + N CALL DLASDT( N, NLVL, ND, IWORK( INODE ), IWORK( NDIML ), \$ IWORK( NDIMR ), SMLSIZ ) * * For the nodes on bottom level of the tree, solve * their subproblems by DLASDQ. * NDB1 = ( ND+1 ) / 2 NCC = 0 DO 30 I = NDB1, ND * * IC : center row of each node * NL : number of rows of left subproblem * NR : number of rows of right subproblem * NLF: starting row of the left subproblem * NRF: starting row of the right subproblem * I1 = I - 1 IC = IWORK( INODE+I1 ) NL = IWORK( NDIML+I1 ) NLP1 = NL + 1 NR = IWORK( NDIMR+I1 ) NRP1 = NR + 1 NLF = IC - NL NRF = IC + 1 SQREI = 1 CALL DLASDQ( 'U', SQREI, NL, NLP1, NL, NCC, D( NLF ), E( NLF ), \$ VT( NLF, NLF ), LDVT, U( NLF, NLF ), LDU, \$ U( NLF, NLF ), LDU, WORK, INFO ) IF( INFO.NE.0 ) THEN RETURN END IF ITEMP = IDXQ + NLF - 2 DO 10 J = 1, NL IWORK( ITEMP+J ) = J 10 CONTINUE IF( I.EQ.ND ) THEN SQREI = SQRE ELSE SQREI = 1 END IF NRP1 = NR + SQREI CALL DLASDQ( 'U', SQREI, NR, NRP1, NR, NCC, D( NRF ), E( NRF ), \$ VT( NRF, NRF ), LDVT, U( NRF, NRF ), LDU, \$ U( NRF, NRF ), LDU, WORK, INFO ) IF( INFO.NE.0 ) THEN RETURN END IF ITEMP = IDXQ + IC DO 20 J = 1, NR IWORK( ITEMP+J-1 ) = J 20 CONTINUE 30 CONTINUE * * Now conquer each subproblem bottom-up. * DO 50 LVL = NLVL, 1, -1 * * Find the first node LF and last node LL on the * current level LVL. * IF( LVL.EQ.1 ) THEN LF = 1 LL = 1 ELSE LF = 2**( LVL-1 ) LL = 2*LF - 1 END IF DO 40 I = LF, LL IM1 = I - 1 IC = IWORK( INODE+IM1 ) NL = IWORK( NDIML+IM1 ) NR = IWORK( NDIMR+IM1 ) NLF = IC - NL IF( ( SQRE.EQ.0 ) .AND. ( I.EQ.LL ) ) THEN SQREI = SQRE ELSE SQREI = 1 END IF IDXQC = IDXQ + NLF - 1 ALPHA = D( IC ) BETA = E( IC ) CALL DLASD1( NL, NR, SQREI, D( NLF ), ALPHA, BETA, \$ U( NLF, NLF ), LDU, VT( NLF, NLF ), LDVT, \$ IWORK( IDXQC ), IWORK( IWK ), WORK, INFO ) IF( INFO.NE.0 ) THEN RETURN END IF 40 CONTINUE 50 CONTINUE * RETURN * * End of DLASD0 * END