SUBROUTINE SLAROT( LROWS, LLEFT, LRIGHT, NL, C, S, A, LDA, XLEFT,
$ XRIGHT )
*
* -- LAPACK auxiliary test routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
LOGICAL LLEFT, LRIGHT, LROWS
INTEGER LDA, NL
REAL C, S, XLEFT, XRIGHT
* ..
* .. Array Arguments ..
REAL A( * )
* ..
*
* Purpose
* =======
*
* SLAROT applies a (Givens) rotation to two adjacent rows or
* columns, where one element of the first and/or last column/row
* for use on matrices stored in some format other than GE, so
* that elements of the matrix may be used or modified for which
* no array element is provided.
*
* One example is a symmetric matrix in SB format (bandwidth=4), for
* which UPLO='L': Two adjacent rows will have the format:
*
* row j: * * * * * . . . .
* row j+1: * * * * * . . . .
*
* '*' indicates elements for which storage is provided,
* '.' indicates elements for which no storage is provided, but
* are not necessarily zero; their values are determined by
* symmetry. ' ' indicates elements which are necessarily zero,
* and have no storage provided.
*
* Those columns which have two '*'s can be handled by SROT.
* Those columns which have no '*'s can be ignored, since as long
* as the Givens rotations are carefully applied to preserve
* symmetry, their values are determined.
* Those columns which have one '*' have to be handled separately,
* by using separate variables "p" and "q":
*
* row j: * * * * * p . . .
* row j+1: q * * * * * . . . .
*
* The element p would have to be set correctly, then that column
* is rotated, setting p to its new value. The next call to
* SLAROT would rotate columns j and j+1, using p, and restore
* symmetry. The element q would start out being zero, and be
* made non-zero by the rotation. Later, rotations would presumably
* be chosen to zero q out.
*
* Typical Calling Sequences: rotating the i-th and (i+1)-st rows.
* ------- ------- ---------
*
* General dense matrix:
*
* CALL SLAROT(.TRUE.,.FALSE.,.FALSE., N, C,S,
* A(i,1),LDA, DUMMY, DUMMY)
*
* General banded matrix in GB format:
*
* j = MAX(1, i-KL )
* NL = MIN( N, i+KU+1 ) + 1-j
* CALL SLAROT( .TRUE., i-KL.GE.1, i+KU.LT.N, NL, C,S,
* A(KU+i+1-j,j),LDA-1, XLEFT, XRIGHT )
*
* [ note that i+1-j is just MIN(i,KL+1) ]
*
* Symmetric banded matrix in SY format, bandwidth K,
* lower triangle only:
*
* j = MAX(1, i-K )
* NL = MIN( K+1, i ) + 1
* CALL SLAROT( .TRUE., i-K.GE.1, .TRUE., NL, C,S,
* A(i,j), LDA, XLEFT, XRIGHT )
*
* Same, but upper triangle only:
*
* NL = MIN( K+1, N-i ) + 1
* CALL SLAROT( .TRUE., .TRUE., i+K.LT.N, NL, C,S,
* A(i,i), LDA, XLEFT, XRIGHT )
*
* Symmetric banded matrix in SB format, bandwidth K,
* lower triangle only:
*
* [ same as for SY, except:]
* . . . .
* A(i+1-j,j), LDA-1, XLEFT, XRIGHT )
*
* [ note that i+1-j is just MIN(i,K+1) ]
*
* Same, but upper triangle only:
* . . .
* A(K+1,i), LDA-1, XLEFT, XRIGHT )
*
* Rotating columns is just the transpose of rotating rows, except
* for GB and SB: (rotating columns i and i+1)
*
* GB:
* j = MAX(1, i-KU )
* NL = MIN( N, i+KL+1 ) + 1-j
* CALL SLAROT( .TRUE., i-KU.GE.1, i+KL.LT.N, NL, C,S,
* A(KU+j+1-i,i),LDA-1, XTOP, XBOTTM )
*
* [note that KU+j+1-i is just MAX(1,KU+2-i)]
*
* SB: (upper triangle)
*
* . . . . . .
* A(K+j+1-i,i),LDA-1, XTOP, XBOTTM )
*
* SB: (lower triangle)
*
* . . . . . .
* A(1,i),LDA-1, XTOP, XBOTTM )
*
* Arguments
* =========
*
* LROWS - LOGICAL
* If .TRUE., then SLAROT will rotate two rows. If .FALSE.,
* then it will rotate two columns.
* Not modified.
*
* LLEFT - LOGICAL
* If .TRUE., then XLEFT will be used instead of the
* corresponding element of A for the first element in the
* second row (if LROWS=.FALSE.) or column (if LROWS=.TRUE.)
* If .FALSE., then the corresponding element of A will be
* used.
* Not modified.
*
* LRIGHT - LOGICAL
* If .TRUE., then XRIGHT will be used instead of the
* corresponding element of A for the last element in the
* first row (if LROWS=.FALSE.) or column (if LROWS=.TRUE.) If
* .FALSE., then the corresponding element of A will be used.
* Not modified.
*
* NL - INTEGER
* The length of the rows (if LROWS=.TRUE.) or columns (if
* LROWS=.FALSE.) to be rotated. If XLEFT and/or XRIGHT are
* used, the columns/rows they are in should be included in
* NL, e.g., if LLEFT = LRIGHT = .TRUE., then NL must be at
* least 2. The number of rows/columns to be rotated
* exclusive of those involving XLEFT and/or XRIGHT may
* not be negative, i.e., NL minus how many of LLEFT and
* LRIGHT are .TRUE. must be at least zero; if not, XERBLA
* will be called.
* Not modified.
*
* C, S - REAL
* Specify the Givens rotation to be applied. If LROWS is
* true, then the matrix ( c s )
* (-s c ) is applied from the left;
* if false, then the transpose thereof is applied from the
* right. For a Givens rotation, C**2 + S**2 should be 1,
* but this is not checked.
* Not modified.
*
* A - REAL array.
* The array containing the rows/columns to be rotated. The
* first element of A should be the upper left element to
* be rotated.
* Read and modified.
*
* LDA - INTEGER
* The "effective" leading dimension of A. If A contains
* a matrix stored in GE or SY format, then this is just
* the leading dimension of A as dimensioned in the calling
* routine. If A contains a matrix stored in band (GB or SB)
* format, then this should be *one less* than the leading
* dimension used in the calling routine. Thus, if
* A were dimensioned A(LDA,*) in SLAROT, then A(1,j) would
* be the j-th element in the first of the two rows
* to be rotated, and A(2,j) would be the j-th in the second,
* regardless of how the array may be stored in the calling
* routine. [A cannot, however, actually be dimensioned thus,
* since for band format, the row number may exceed LDA, which
* is not legal FORTRAN.]
* If LROWS=.TRUE., then LDA must be at least 1, otherwise
* it must be at least NL minus the number of .TRUE. values
* in XLEFT and XRIGHT.
* Not modified.
*
* XLEFT - REAL
* If LLEFT is .TRUE., then XLEFT will be used and modified
* instead of A(2,1) (if LROWS=.TRUE.) or A(1,2)
* (if LROWS=.FALSE.).
* Read and modified.
*
* XRIGHT - REAL
* If LRIGHT is .TRUE., then XRIGHT will be used and modified
* instead of A(1,NL) (if LROWS=.TRUE.) or A(NL,1)
* (if LROWS=.FALSE.).
* Read and modified.
*
* =====================================================================
*
* .. Local Scalars ..
INTEGER IINC, INEXT, IX, IY, IYT, NT
* ..
* .. Local Arrays ..
REAL XT( 2 ), YT( 2 )
* ..
* .. External Subroutines ..
EXTERNAL SROT, XERBLA
* ..
* .. Executable Statements ..
*
* Set up indices, arrays for ends
*
IF( LROWS ) THEN
IINC = LDA
INEXT = 1
ELSE
IINC = 1
INEXT = LDA
END IF
*
IF( LLEFT ) THEN
NT = 1
IX = 1 + IINC
IY = 2 + LDA
XT( 1 ) = A( 1 )
YT( 1 ) = XLEFT
ELSE
NT = 0
IX = 1
IY = 1 + INEXT
END IF
*
IF( LRIGHT ) THEN
IYT = 1 + INEXT + ( NL-1 )*IINC
NT = NT + 1
XT( NT ) = XRIGHT
YT( NT ) = A( IYT )
END IF
*
* Check for errors
*
IF( NL.LT.NT ) THEN
CALL XERBLA( 'SLAROT', 4 )
RETURN
END IF
IF( LDA.LE.0 .OR. ( .NOT.LROWS .AND. LDA.LT.NL-NT ) ) THEN
CALL XERBLA( 'SLAROT', 8 )
RETURN
END IF
*
* Rotate
*
CALL SROT( NL-NT, A( IX ), IINC, A( IY ), IINC, C, S )
CALL SROT( NT, XT, 1, YT, 1, C, S )
*
* Stuff values back into XLEFT, XRIGHT, etc.
*
IF( LLEFT ) THEN
A( 1 ) = XT( 1 )
XLEFT = YT( 1 )
END IF
*
IF( LRIGHT ) THEN
XRIGHT = XT( NT )
A( IYT ) = YT( NT )
END IF
*
RETURN
*
* End of SLAROT
*
END