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SUBROUTINE DOPGTR( UPLO, N, AP, TAU, Q, LDQ, WORK, INFO )
* * -- LAPACK 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 .. CHARACTER UPLO INTEGER INFO, LDQ, N * .. * .. Array Arguments .. DOUBLE PRECISION AP( * ), Q( LDQ, * ), TAU( * ), WORK( * ) * .. * * Purpose * ======= * * DOPGTR generates a real orthogonal matrix Q which is defined as the * product of n-1 elementary reflectors H(i) of order n, as returned by * DSPTRD using packed storage: * * if UPLO = 'U', Q = H(n-1) . . . H(2) H(1), * * if UPLO = 'L', Q = H(1) H(2) . . . H(n-1). * * Arguments * ========= * * UPLO (input) CHARACTER*1 * = 'U': Upper triangular packed storage used in previous * call to DSPTRD; * = 'L': Lower triangular packed storage used in previous * call to DSPTRD. * * N (input) INTEGER * The order of the matrix Q. N >= 0. * * AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2) * The vectors which define the elementary reflectors, as * returned by DSPTRD. * * TAU (input) DOUBLE PRECISION array, dimension (N-1) * TAU(i) must contain the scalar factor of the elementary * reflector H(i), as returned by DSPTRD. * * Q (output) DOUBLE PRECISION array, dimension (LDQ,N) * The N-by-N orthogonal matrix Q. * * LDQ (input) INTEGER * The leading dimension of the array Q. LDQ >= max(1,N). * * WORK (workspace) DOUBLE PRECISION array, dimension (N-1) * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -i, the i-th argument had an illegal value * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ZERO, ONE PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 ) * .. * .. Local Scalars .. LOGICAL UPPER INTEGER I, IINFO, IJ, J * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL DORG2L, DORG2R, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * Test the input arguments * INFO = 0 UPPER = LSAME( UPLO, 'U' ) IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( LDQ.LT.MAX( 1, N ) ) THEN INFO = -6 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'DOPGTR', -INFO ) RETURN END IF * * Quick return if possible * IF( N.EQ.0 ) $ RETURN * IF( UPPER ) THEN * * Q was determined by a call to DSPTRD with UPLO = 'U' * * Unpack the vectors which define the elementary reflectors and * set the last row and column of Q equal to those of the unit * matrix * IJ = 2 DO 20 J = 1, N - 1 DO 10 I = 1, J - 1 Q( I, J ) = AP( IJ ) IJ = IJ + 1 10 CONTINUE IJ = IJ + 2 Q( N, J ) = ZERO 20 CONTINUE DO 30 I = 1, N - 1 Q( I, N ) = ZERO 30 CONTINUE Q( N, N ) = ONE * * Generate Q(1:n-1,1:n-1) * CALL DORG2L( N-1, N-1, N-1, Q, LDQ, TAU, WORK, IINFO ) * ELSE * * Q was determined by a call to DSPTRD with UPLO = 'L'. * * Unpack the vectors which define the elementary reflectors and * set the first row and column of Q equal to those of the unit * matrix * Q( 1, 1 ) = ONE DO 40 I = 2, N Q( I, 1 ) = ZERO 40 CONTINUE IJ = 3 DO 60 J = 2, N Q( 1, J ) = ZERO DO 50 I = J + 1, N Q( I, J ) = AP( IJ ) IJ = IJ + 1 50 CONTINUE IJ = IJ + 2 60 CONTINUE IF( N.GT.1 ) THEN * * Generate Q(2:n,2:n) * CALL DORG2R( N-1, N-1, N-1, Q( 2, 2 ), LDQ, TAU, WORK, $ IINFO ) END IF END IF RETURN * * End of DOPGTR * END |