Annotation of rpl/lapack/lapack/zung2l.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE ZUNG2L( M, N, K, A, LDA, TAU, WORK, INFO )
! 2: *
! 3: * -- LAPACK routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: INTEGER INFO, K, LDA, M, N
! 10: * ..
! 11: * .. Array Arguments ..
! 12: COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
! 13: * ..
! 14: *
! 15: * Purpose
! 16: * =======
! 17: *
! 18: * ZUNG2L generates an m by n complex matrix Q with orthonormal columns,
! 19: * which is defined as the last n columns of a product of k elementary
! 20: * reflectors of order m
! 21: *
! 22: * Q = H(k) . . . H(2) H(1)
! 23: *
! 24: * as returned by ZGEQLF.
! 25: *
! 26: * Arguments
! 27: * =========
! 28: *
! 29: * M (input) INTEGER
! 30: * The number of rows of the matrix Q. M >= 0.
! 31: *
! 32: * N (input) INTEGER
! 33: * The number of columns of the matrix Q. M >= N >= 0.
! 34: *
! 35: * K (input) INTEGER
! 36: * The number of elementary reflectors whose product defines the
! 37: * matrix Q. N >= K >= 0.
! 38: *
! 39: * A (input/output) COMPLEX*16 array, dimension (LDA,N)
! 40: * On entry, the (n-k+i)-th column must contain the vector which
! 41: * defines the elementary reflector H(i), for i = 1,2,...,k, as
! 42: * returned by ZGEQLF in the last k columns of its array
! 43: * argument A.
! 44: * On exit, the m-by-n matrix Q.
! 45: *
! 46: * LDA (input) INTEGER
! 47: * The first dimension of the array A. LDA >= max(1,M).
! 48: *
! 49: * TAU (input) COMPLEX*16 array, dimension (K)
! 50: * TAU(i) must contain the scalar factor of the elementary
! 51: * reflector H(i), as returned by ZGEQLF.
! 52: *
! 53: * WORK (workspace) COMPLEX*16 array, dimension (N)
! 54: *
! 55: * INFO (output) INTEGER
! 56: * = 0: successful exit
! 57: * < 0: if INFO = -i, the i-th argument has an illegal value
! 58: *
! 59: * =====================================================================
! 60: *
! 61: * .. Parameters ..
! 62: COMPLEX*16 ONE, ZERO
! 63: PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ),
! 64: $ ZERO = ( 0.0D+0, 0.0D+0 ) )
! 65: * ..
! 66: * .. Local Scalars ..
! 67: INTEGER I, II, J, L
! 68: * ..
! 69: * .. External Subroutines ..
! 70: EXTERNAL XERBLA, ZLARF, ZSCAL
! 71: * ..
! 72: * .. Intrinsic Functions ..
! 73: INTRINSIC MAX
! 74: * ..
! 75: * .. Executable Statements ..
! 76: *
! 77: * Test the input arguments
! 78: *
! 79: INFO = 0
! 80: IF( M.LT.0 ) THEN
! 81: INFO = -1
! 82: ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
! 83: INFO = -2
! 84: ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
! 85: INFO = -3
! 86: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
! 87: INFO = -5
! 88: END IF
! 89: IF( INFO.NE.0 ) THEN
! 90: CALL XERBLA( 'ZUNG2L', -INFO )
! 91: RETURN
! 92: END IF
! 93: *
! 94: * Quick return if possible
! 95: *
! 96: IF( N.LE.0 )
! 97: $ RETURN
! 98: *
! 99: * Initialise columns 1:n-k to columns of the unit matrix
! 100: *
! 101: DO 20 J = 1, N - K
! 102: DO 10 L = 1, M
! 103: A( L, J ) = ZERO
! 104: 10 CONTINUE
! 105: A( M-N+J, J ) = ONE
! 106: 20 CONTINUE
! 107: *
! 108: DO 40 I = 1, K
! 109: II = N - K + I
! 110: *
! 111: * Apply H(i) to A(1:m-k+i,1:n-k+i) from the left
! 112: *
! 113: A( M-N+II, II ) = ONE
! 114: CALL ZLARF( 'Left', M-N+II, II-1, A( 1, II ), 1, TAU( I ), A,
! 115: $ LDA, WORK )
! 116: CALL ZSCAL( M-N+II-1, -TAU( I ), A( 1, II ), 1 )
! 117: A( M-N+II, II ) = ONE - TAU( I )
! 118: *
! 119: * Set A(m-k+i+1:m,n-k+i) to zero
! 120: *
! 121: DO 30 L = M - N + II + 1, M
! 122: A( L, II ) = ZERO
! 123: 30 CONTINUE
! 124: 40 CONTINUE
! 125: RETURN
! 126: *
! 127: * End of ZUNG2L
! 128: *
! 129: END
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