184 lines
5.1 KiB
FortranFixed
184 lines
5.1 KiB
FortranFixed
SUBROUTINE SORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
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*
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* -- LAPACK routine (version 3.1) --
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* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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* November 2006
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*
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* .. Scalar Arguments ..
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CHARACTER UPLO
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INTEGER INFO, LDA, LWORK, N
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* ..
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* .. Array Arguments ..
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REAL A( LDA, * ), TAU( * ), 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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* SORGTR generates a real orthogonal matrix Q which is defined as the
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* product of n-1 elementary reflectors of order N, as returned by
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* SSYTRD:
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*
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* if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
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*
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* if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
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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': Upper triangle of A contains elementary reflectors
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* from SSYTRD;
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* = 'L': Lower triangle of A contains elementary reflectors
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* from SSYTRD.
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*
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* N (input) INTEGER
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* The order of the matrix Q. N >= 0.
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*
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* A (input/output) REAL array, dimension (LDA,N)
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* On entry, the vectors which define the elementary reflectors,
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* as returned by SSYTRD.
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* On exit, the N-by-N orthogonal matrix Q.
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*
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* LDA (input) INTEGER
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* The leading dimension of the array A. LDA >= max(1,N).
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*
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* TAU (input) REAL array, dimension (N-1)
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* TAU(i) must contain the scalar factor of the elementary
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* reflector H(i), as returned by SSYTRD.
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*
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* WORK (workspace/output) REAL array, dimension (MAX(1,LWORK))
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* On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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*
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* LWORK (input) INTEGER
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* The dimension of the array WORK. LWORK >= max(1,N-1).
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* For optimum performance LWORK >= (N-1)*NB, where NB is
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* the optimal blocksize.
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*
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* If LWORK = -1, then a workspace query is assumed; the routine
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* only calculates the optimal size of the WORK array, returns
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* this value as the first entry of the WORK array, and no error
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* message related to LWORK is issued by XERBLA.
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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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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ZERO, ONE
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PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL LQUERY, UPPER
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INTEGER I, IINFO, J, LWKOPT, NB
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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INTEGER ILAENV
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EXTERNAL ILAENV, LSAME
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* ..
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* .. External Subroutines ..
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EXTERNAL SORGQL, SORGQR, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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* .. Executable Statements ..
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*
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* Test the input arguments
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*
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INFO = 0
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LQUERY = ( LWORK.EQ.-1 )
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UPPER = LSAME( UPLO, 'U' )
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IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) 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( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -4
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ELSE IF( LWORK.LT.MAX( 1, N-1 ) .AND. .NOT.LQUERY ) THEN
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INFO = -7
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END IF
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*
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IF( INFO.EQ.0 ) THEN
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IF ( UPPER ) THEN
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NB = ILAENV( 1, 'SORGQL', ' ', N-1, N-1, N-1, -1 )
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ELSE
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NB = ILAENV( 1, 'SORGQR', ' ', N-1, N-1, N-1, -1 )
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END IF
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LWKOPT = MAX( 1, N-1 )*NB
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WORK( 1 ) = LWKOPT
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END IF
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*
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SORGTR', -INFO )
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RETURN
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ELSE IF( LQUERY ) THEN
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RETURN
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END IF
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*
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* Quick return if possible
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*
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IF( N.EQ.0 ) THEN
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WORK( 1 ) = 1
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RETURN
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END IF
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*
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IF( UPPER ) THEN
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*
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* Q was determined by a call to SSYTRD with UPLO = 'U'
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*
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* Shift the vectors which define the elementary reflectors one
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* column to the left, and set the last row and column of Q to
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* those of the unit matrix
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*
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DO 20 J = 1, N - 1
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DO 10 I = 1, J - 1
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A( I, J ) = A( I, J+1 )
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10 CONTINUE
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A( N, J ) = ZERO
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20 CONTINUE
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DO 30 I = 1, N - 1
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A( I, N ) = ZERO
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30 CONTINUE
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A( N, N ) = ONE
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*
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* Generate Q(1:n-1,1:n-1)
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*
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CALL SORGQL( N-1, N-1, N-1, A, LDA, TAU, WORK, LWORK, IINFO )
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*
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ELSE
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*
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* Q was determined by a call to SSYTRD with UPLO = 'L'.
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*
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* Shift the vectors which define the elementary reflectors one
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* column to the right, and set the first row and column of Q to
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* those of the unit matrix
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*
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DO 50 J = N, 2, -1
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A( 1, J ) = ZERO
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DO 40 I = J + 1, N
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A( I, J ) = A( I, J-1 )
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40 CONTINUE
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50 CONTINUE
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A( 1, 1 ) = ONE
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DO 60 I = 2, N
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A( I, 1 ) = ZERO
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60 CONTINUE
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IF( N.GT.1 ) THEN
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*
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* Generate Q(2:n,2:n)
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*
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CALL SORGQR( N-1, N-1, N-1, A( 2, 2 ), LDA, TAU, WORK,
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$ LWORK, IINFO )
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END IF
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END IF
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WORK( 1 ) = LWKOPT
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RETURN
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*
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* End of SORGTR
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*
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END
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