Provided by: liblapack-doc_3.12.0-3build1.1_all bug

NAME

       lasd7 - lasd7: D&C step: deflation

SYNOPSIS

   Functions
       subroutine dlasd7 (icompq, nl, nr, sqre, k, d, z, zw, vf, vfw, vl, vlw, alpha, beta,
           dsigma, idx, idxp, idxq, perm, givptr, givcol, ldgcol, givnum, ldgnum, c, s, info)
           DLASD7 merges the two sets of singular values together into a single sorted set. Then
           it tries to deflate the size of the problem. Used by sbdsdc.
       subroutine slasd7 (icompq, nl, nr, sqre, k, d, z, zw, vf, vfw, vl, vlw, alpha, beta,
           dsigma, idx, idxp, idxq, perm, givptr, givcol, ldgcol, givnum, ldgnum, c, s, info)
           SLASD7 merges the two sets of singular values together into a single sorted set. Then
           it tries to deflate the size of the problem. Used by sbdsdc.

Detailed Description

Function Documentation

   subroutine dlasd7 (integer icompq, integer nl, integer nr, integer sqre, integer k, double
       precision, dimension( * ) d, double precision, dimension( * ) z, double precision,
       dimension( * ) zw, double precision, dimension( * ) vf, double precision, dimension( * )
       vfw, double precision, dimension( * ) vl, double precision, dimension( * ) vlw, double
       precision alpha, double precision beta, double precision, dimension( * ) dsigma, integer,
       dimension( * ) idx, integer, dimension( * ) idxp, integer, dimension( * ) idxq, integer,
       dimension( * ) perm, integer givptr, integer, dimension( ldgcol, * ) givcol, integer
       ldgcol, double precision, dimension( ldgnum, * ) givnum, integer ldgnum, double precision
       c, double precision s, integer info)
       DLASD7 merges the two sets of singular values together into a single sorted set. Then it
       tries to deflate the size of the problem. Used by sbdsdc.

       Purpose:

            DLASD7 merges the two sets of singular values together into a single
            sorted set. Then it tries to deflate the size of the problem. There
            are two ways in which deflation can occur:  when two or more singular
            values are close together or if there is a tiny entry in the Z
            vector. For each such occurrence the order of the related
            secular equation problem is reduced by one.

            DLASD7 is called from DLASD6.

       Parameters
           ICOMPQ

                     ICOMPQ is INTEGER
                     Specifies whether singular vectors are to be computed
                     in compact form, as follows:
                     = 0: Compute singular values only.
                     = 1: Compute singular vectors of upper
                          bidiagonal matrix in compact form.

           NL

                     NL is INTEGER
                    The row dimension of the upper block. NL >= 1.

           NR

                     NR is INTEGER
                    The row dimension of the lower block. NR >= 1.

           SQRE

                     SQRE is INTEGER
                    = 0: the lower block is an NR-by-NR square matrix.
                    = 1: the lower block is an NR-by-(NR+1) rectangular matrix.

                    The bidiagonal matrix has
                    N = NL + NR + 1 rows and
                    M = N + SQRE >= N columns.

           K

                     K is INTEGER
                    Contains the dimension of the non-deflated matrix, this is
                    the order of the related secular equation. 1 <= K <=N.

           D

                     D is DOUBLE PRECISION array, dimension ( N )
                    On entry D contains the singular values of the two submatrices
                    to be combined. On exit D contains the trailing (N-K) updated
                    singular values (those which were deflated) sorted into
                    increasing order.

           Z

                     Z is DOUBLE PRECISION array, dimension ( M )
                    On exit Z contains the updating row vector in the secular
                    equation.

           ZW

                     ZW is DOUBLE PRECISION array, dimension ( M )
                    Workspace for Z.

           VF

                     VF is DOUBLE PRECISION array, dimension ( M )
                    On entry, VF(1:NL+1) contains the first components of all
                    right singular vectors of the upper block; and VF(NL+2:M)
                    contains the first components of all right singular vectors
                    of the lower block. On exit, VF contains the first components
                    of all right singular vectors of the bidiagonal matrix.

           VFW

                     VFW is DOUBLE PRECISION array, dimension ( M )
                    Workspace for VF.

           VL

                     VL is DOUBLE PRECISION array, dimension ( M )
                    On entry, VL(1:NL+1) contains the  last components of all
                    right singular vectors of the upper block; and VL(NL+2:M)
                    contains the last components of all right singular vectors
                    of the lower block. On exit, VL contains the last components
                    of all right singular vectors of the bidiagonal matrix.

           VLW

                     VLW is DOUBLE PRECISION array, dimension ( M )
                    Workspace for VL.

           ALPHA

                     ALPHA is DOUBLE PRECISION
                    Contains the diagonal element associated with the added row.

           BETA

                     BETA is DOUBLE PRECISION
                    Contains the off-diagonal element associated with the added
                    row.

           DSIGMA

                     DSIGMA is DOUBLE PRECISION array, dimension ( N )
                    Contains a copy of the diagonal elements (K-1 singular values
                    and one zero) in the secular equation.

           IDX

                     IDX is INTEGER array, dimension ( N )
                    This will contain the permutation used to sort the contents of
                    D into ascending order.

           IDXP

                     IDXP is INTEGER array, dimension ( N )
                    This will contain the permutation used to place deflated
                    values of D at the end of the array. On output IDXP(2:K)
                    points to the nondeflated D-values and IDXP(K+1:N)
                    points to the deflated singular values.

           IDXQ

                     IDXQ is INTEGER array, dimension ( N )
                    This contains the permutation which separately sorts the two
                    sub-problems in D into ascending order.  Note that entries in
                    the first half of this permutation must first be moved one
                    position backward; and entries in the second half
                    must first have NL+1 added to their values.

           PERM

                     PERM is INTEGER array, dimension ( N )
                    The permutations (from deflation and sorting) to be applied
                    to each singular block. Not referenced if ICOMPQ = 0.

           GIVPTR

                     GIVPTR is INTEGER
                    The number of Givens rotations which took place in this
                    subproblem. Not referenced if ICOMPQ = 0.

           GIVCOL

                     GIVCOL is INTEGER array, dimension ( LDGCOL, 2 )
                    Each pair of numbers indicates a pair of columns to take place
                    in a Givens rotation. Not referenced if ICOMPQ = 0.

           LDGCOL

                     LDGCOL is INTEGER
                    The leading dimension of GIVCOL, must be at least N.

           GIVNUM

                     GIVNUM is DOUBLE PRECISION array, dimension ( LDGNUM, 2 )
                    Each number indicates the C or S value to be used in the
                    corresponding Givens rotation. Not referenced if ICOMPQ = 0.

           LDGNUM

                     LDGNUM is INTEGER
                    The leading dimension of GIVNUM, must be at least N.

           C

                     C is DOUBLE PRECISION
                    C contains garbage if SQRE =0 and the C-value of a Givens
                    rotation related to the right null space if SQRE = 1.

           S

                     S is DOUBLE PRECISION
                    S contains garbage if SQRE =0 and the S-value of a Givens
                    rotation related to the right null space if SQRE = 1.

           INFO

                     INFO is INTEGER
                    = 0:  successful exit.
                    < 0:  if INFO = -i, the i-th argument had an illegal value.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Contributors:
           Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley,
           USA

   subroutine slasd7 (integer icompq, integer nl, integer nr, integer sqre, integer k, real,
       dimension( * ) d, real, dimension( * ) z, real, dimension( * ) zw, real, dimension( * )
       vf, real, dimension( * ) vfw, real, dimension( * ) vl, real, dimension( * ) vlw, real
       alpha, real beta, real, dimension( * ) dsigma, integer, dimension( * ) idx, integer,
       dimension( * ) idxp, integer, dimension( * ) idxq, integer, dimension( * ) perm, integer
       givptr, integer, dimension( ldgcol, * ) givcol, integer ldgcol, real, dimension( ldgnum, *
       ) givnum, integer ldgnum, real c, real s, integer info)
       SLASD7 merges the two sets of singular values together into a single sorted set. Then it
       tries to deflate the size of the problem. Used by sbdsdc.

       Purpose:

            SLASD7 merges the two sets of singular values together into a single
            sorted set. Then it tries to deflate the size of the problem. There
            are two ways in which deflation can occur:  when two or more singular
            values are close together or if there is a tiny entry in the Z
            vector. For each such occurrence the order of the related
            secular equation problem is reduced by one.

            SLASD7 is called from SLASD6.

       Parameters
           ICOMPQ

                     ICOMPQ is INTEGER
                     Specifies whether singular vectors are to be computed
                     in compact form, as follows:
                     = 0: Compute singular values only.
                     = 1: Compute singular vectors of upper
                          bidiagonal matrix in compact form.

           NL

                     NL is INTEGER
                    The row dimension of the upper block. NL >= 1.

           NR

                     NR is INTEGER
                    The row dimension of the lower block. NR >= 1.

           SQRE

                     SQRE is INTEGER
                    = 0: the lower block is an NR-by-NR square matrix.
                    = 1: the lower block is an NR-by-(NR+1) rectangular matrix.

                    The bidiagonal matrix has
                    N = NL + NR + 1 rows and
                    M = N + SQRE >= N columns.

           K

                     K is INTEGER
                    Contains the dimension of the non-deflated matrix, this is
                    the order of the related secular equation. 1 <= K <=N.

           D

                     D is REAL array, dimension ( N )
                    On entry D contains the singular values of the two submatrices
                    to be combined. On exit D contains the trailing (N-K) updated
                    singular values (those which were deflated) sorted into
                    increasing order.

           Z

                     Z is REAL array, dimension ( M )
                    On exit Z contains the updating row vector in the secular
                    equation.

           ZW

                     ZW is REAL array, dimension ( M )
                    Workspace for Z.

           VF

                     VF is REAL array, dimension ( M )
                    On entry, VF(1:NL+1) contains the first components of all
                    right singular vectors of the upper block; and VF(NL+2:M)
                    contains the first components of all right singular vectors
                    of the lower block. On exit, VF contains the first components
                    of all right singular vectors of the bidiagonal matrix.

           VFW

                     VFW is REAL array, dimension ( M )
                    Workspace for VF.

           VL

                     VL is REAL array, dimension ( M )
                    On entry, VL(1:NL+1) contains the  last components of all
                    right singular vectors of the upper block; and VL(NL+2:M)
                    contains the last components of all right singular vectors
                    of the lower block. On exit, VL contains the last components
                    of all right singular vectors of the bidiagonal matrix.

           VLW

                     VLW is REAL array, dimension ( M )
                    Workspace for VL.

           ALPHA

                     ALPHA is REAL
                    Contains the diagonal element associated with the added row.

           BETA

                     BETA is REAL
                    Contains the off-diagonal element associated with the added
                    row.

           DSIGMA

                     DSIGMA is REAL array, dimension ( N )
                    Contains a copy of the diagonal elements (K-1 singular values
                    and one zero) in the secular equation.

           IDX

                     IDX is INTEGER array, dimension ( N )
                    This will contain the permutation used to sort the contents of
                    D into ascending order.

           IDXP

                     IDXP is INTEGER array, dimension ( N )
                    This will contain the permutation used to place deflated
                    values of D at the end of the array. On output IDXP(2:K)
                    points to the nondeflated D-values and IDXP(K+1:N)
                    points to the deflated singular values.

           IDXQ

                     IDXQ is INTEGER array, dimension ( N )
                    This contains the permutation which separately sorts the two
                    sub-problems in D into ascending order.  Note that entries in
                    the first half of this permutation must first be moved one
                    position backward; and entries in the second half
                    must first have NL+1 added to their values.

           PERM

                     PERM is INTEGER array, dimension ( N )
                    The permutations (from deflation and sorting) to be applied
                    to each singular block. Not referenced if ICOMPQ = 0.

           GIVPTR

                     GIVPTR is INTEGER
                    The number of Givens rotations which took place in this
                    subproblem. Not referenced if ICOMPQ = 0.

           GIVCOL

                     GIVCOL is INTEGER array, dimension ( LDGCOL, 2 )
                    Each pair of numbers indicates a pair of columns to take place
                    in a Givens rotation. Not referenced if ICOMPQ = 0.

           LDGCOL

                     LDGCOL is INTEGER
                    The leading dimension of GIVCOL, must be at least N.

           GIVNUM

                     GIVNUM is REAL array, dimension ( LDGNUM, 2 )
                    Each number indicates the C or S value to be used in the
                    corresponding Givens rotation. Not referenced if ICOMPQ = 0.

           LDGNUM

                     LDGNUM is INTEGER
                    The leading dimension of GIVNUM, must be at least N.

           C

                     C is REAL
                    C contains garbage if SQRE =0 and the C-value of a Givens
                    rotation related to the right null space if SQRE = 1.

           S

                     S is REAL
                    S contains garbage if SQRE =0 and the S-value of a Givens
                    rotation related to the right null space if SQRE = 1.

           INFO

                     INFO is INTEGER
                    = 0:  successful exit.
                    < 0:  if INFO = -i, the i-th argument had an illegal value.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Contributors:
           Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley,
           USA

Author

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