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annotate libcruft/lapack/sorg2r.f @ 7948:af10baa63915 ss-3-1-50

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3.1.50 snapshot
author John W. Eaton <jwe@octave.org>
date Fri, 18 Jul 2008 17:42:48 -0400
parents 82be108cc558
children
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1 SUBROUTINE SORG2R( M, N, K, A, LDA, TAU, WORK, INFO )
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2 *
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3 * -- LAPACK routine (version 3.1) --
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4 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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5 * November 2006
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6 *
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7 * .. Scalar Arguments ..
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8 INTEGER INFO, K, LDA, M, N
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9 * ..
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10 * .. Array Arguments ..
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11 REAL A( LDA, * ), TAU( * ), WORK( * )
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12 * ..
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13 *
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14 * Purpose
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15 * =======
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16 *
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17 * SORG2R generates an m by n real matrix Q with orthonormal columns,
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18 * which is defined as the first n columns of a product of k elementary
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19 * reflectors of order m
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20 *
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21 * Q = H(1) H(2) . . . H(k)
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22 *
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23 * as returned by SGEQRF.
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24 *
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25 * Arguments
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26 * =========
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27 *
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28 * M (input) INTEGER
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29 * The number of rows of the matrix Q. M >= 0.
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30 *
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31 * N (input) INTEGER
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32 * The number of columns of the matrix Q. M >= N >= 0.
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33 *
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34 * K (input) INTEGER
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35 * The number of elementary reflectors whose product defines the
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36 * matrix Q. N >= K >= 0.
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37 *
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38 * A (input/output) REAL array, dimension (LDA,N)
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39 * On entry, the i-th column must contain the vector which
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40 * defines the elementary reflector H(i), for i = 1,2,...,k, as
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41 * returned by SGEQRF in the first k columns of its array
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42 * argument A.
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43 * On exit, the m-by-n matrix Q.
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44 *
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45 * LDA (input) INTEGER
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46 * The first dimension of the array A. LDA >= max(1,M).
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47 *
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48 * TAU (input) REAL array, dimension (K)
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49 * TAU(i) must contain the scalar factor of the elementary
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50 * reflector H(i), as returned by SGEQRF.
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51 *
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52 * WORK (workspace) REAL array, dimension (N)
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53 *
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54 * INFO (output) INTEGER
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55 * = 0: successful exit
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56 * < 0: if INFO = -i, the i-th argument has an illegal value
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57 *
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58 * =====================================================================
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59 *
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60 * .. Parameters ..
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61 REAL ONE, ZERO
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62 PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
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63 * ..
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64 * .. Local Scalars ..
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65 INTEGER I, J, L
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66 * ..
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67 * .. External Subroutines ..
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68 EXTERNAL SLARF, SSCAL, XERBLA
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69 * ..
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70 * .. Intrinsic Functions ..
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71 INTRINSIC MAX
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72 * ..
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73 * .. Executable Statements ..
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74 *
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75 * Test the input arguments
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76 *
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77 INFO = 0
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78 IF( M.LT.0 ) THEN
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79 INFO = -1
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80 ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
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81 INFO = -2
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82 ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
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83 INFO = -3
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84 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
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85 INFO = -5
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86 END IF
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87 IF( INFO.NE.0 ) THEN
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88 CALL XERBLA( 'SORG2R', -INFO )
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89 RETURN
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90 END IF
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91 *
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92 * Quick return if possible
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93 *
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94 IF( N.LE.0 )
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95 $ RETURN
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96 *
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97 * Initialise columns k+1:n to columns of the unit matrix
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98 *
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99 DO 20 J = K + 1, N
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100 DO 10 L = 1, M
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101 A( L, J ) = ZERO
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102 10 CONTINUE
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103 A( J, J ) = ONE
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104 20 CONTINUE
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105 *
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106 DO 40 I = K, 1, -1
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107 *
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108 * Apply H(i) to A(i:m,i:n) from the left
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109 *
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110 IF( I.LT.N ) THEN
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111 A( I, I ) = ONE
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112 CALL SLARF( 'Left', M-I+1, N-I, A( I, I ), 1, TAU( I ),
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113 $ A( I, I+1 ), LDA, WORK )
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114 END IF
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115 IF( I.LT.M )
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116 $ CALL SSCAL( M-I, -TAU( I ), A( I+1, I ), 1 )
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117 A( I, I ) = ONE - TAU( I )
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118 *
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119 * Set A(1:i-1,i) to zero
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120 *
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121 DO 30 L = 1, I - 1
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122 A( L, I ) = ZERO
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123 30 CONTINUE
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124 40 CONTINUE
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125 RETURN
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126 *
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127 * End of SORG2R
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128 *
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129 END