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annotate libcruft/lapack/ctrti2.f @ 7789:82be108cc558

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First attempt at single precision tyeps * * * corrections to qrupdate single precision routines * * * prefer demotion to single over promotion to double * * * Add single precision support to log2 function * * * Trivial PROJECT file update * * * Cache optimized hermitian/transpose methods * * * Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author David Bateman <dbateman@free.fr>
date Sun, 27 Apr 2008 22:34:17 +0200
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7789
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1 SUBROUTINE CTRTI2( UPLO, DIAG, N, A, LDA, 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 CHARACTER DIAG, UPLO
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9 INTEGER INFO, LDA, N
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10 * ..
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11 * .. Array Arguments ..
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12 COMPLEX A( LDA, * )
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13 * ..
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14 *
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15 * Purpose
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16 * =======
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17 *
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18 * CTRTI2 computes the inverse of a complex upper or lower triangular
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19 * matrix.
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20 *
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21 * This is the Level 2 BLAS version of the algorithm.
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22 *
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23 * Arguments
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24 * =========
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25 *
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26 * UPLO (input) CHARACTER*1
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27 * Specifies whether the matrix A is upper or lower triangular.
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28 * = 'U': Upper triangular
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29 * = 'L': Lower triangular
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30 *
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31 * DIAG (input) CHARACTER*1
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32 * Specifies whether or not the matrix A is unit triangular.
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33 * = 'N': Non-unit triangular
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34 * = 'U': Unit triangular
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35 *
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36 * N (input) INTEGER
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37 * The order of the matrix A. N >= 0.
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38 *
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39 * A (input/output) COMPLEX array, dimension (LDA,N)
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40 * On entry, the triangular matrix A. If UPLO = 'U', the
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41 * leading n by n upper triangular part of the array A contains
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42 * the upper triangular matrix, and the strictly lower
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43 * triangular part of A is not referenced. If UPLO = 'L', the
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44 * leading n by n lower triangular part of the array A contains
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45 * the lower triangular matrix, and the strictly upper
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46 * triangular part of A is not referenced. If DIAG = 'U', the
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47 * diagonal elements of A are also not referenced and are
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48 * assumed to be 1.
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49 *
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50 * On exit, the (triangular) inverse of the original matrix, in
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51 * the same storage format.
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52 *
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53 * LDA (input) INTEGER
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54 * The leading dimension of the array A. LDA >= max(1,N).
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55 *
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56 * INFO (output) INTEGER
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57 * = 0: successful exit
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58 * < 0: if INFO = -k, the k-th argument had an illegal value
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59 *
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60 * =====================================================================
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61 *
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62 * .. Parameters ..
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63 COMPLEX ONE
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64 PARAMETER ( ONE = ( 1.0E+0, 0.0E+0 ) )
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65 * ..
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66 * .. Local Scalars ..
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67 LOGICAL NOUNIT, UPPER
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68 INTEGER J
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69 COMPLEX AJJ
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70 * ..
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71 * .. External Functions ..
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72 LOGICAL LSAME
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73 EXTERNAL LSAME
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74 * ..
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75 * .. External Subroutines ..
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76 EXTERNAL CSCAL, CTRMV, XERBLA
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77 * ..
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78 * .. Intrinsic Functions ..
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79 INTRINSIC MAX
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80 * ..
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81 * .. Executable Statements ..
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82 *
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83 * Test the input parameters.
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84 *
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85 INFO = 0
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86 UPPER = LSAME( UPLO, 'U' )
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87 NOUNIT = LSAME( DIAG, 'N' )
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88 IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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89 INFO = -1
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90 ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
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91 INFO = -2
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92 ELSE IF( N.LT.0 ) THEN
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93 INFO = -3
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94 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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95 INFO = -5
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96 END IF
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97 IF( INFO.NE.0 ) THEN
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98 CALL XERBLA( 'CTRTI2', -INFO )
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99 RETURN
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100 END IF
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101 *
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102 IF( UPPER ) THEN
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103 *
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104 * Compute inverse of upper triangular matrix.
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105 *
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106 DO 10 J = 1, N
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107 IF( NOUNIT ) THEN
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108 A( J, J ) = ONE / A( J, J )
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109 AJJ = -A( J, J )
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110 ELSE
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111 AJJ = -ONE
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112 END IF
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113 *
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114 * Compute elements 1:j-1 of j-th column.
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115 *
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116 CALL CTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA,
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117 $ A( 1, J ), 1 )
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118 CALL CSCAL( J-1, AJJ, A( 1, J ), 1 )
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119 10 CONTINUE
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120 ELSE
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121 *
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122 * Compute inverse of lower triangular matrix.
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123 *
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124 DO 20 J = N, 1, -1
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125 IF( NOUNIT ) THEN
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126 A( J, J ) = ONE / A( J, J )
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127 AJJ = -A( J, J )
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128 ELSE
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129 AJJ = -ONE
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130 END IF
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131 IF( J.LT.N ) THEN
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132 *
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133 * Compute elements j+1:n of j-th column.
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134 *
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135 CALL CTRMV( 'Lower', 'No transpose', DIAG, N-J,
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136 $ A( J+1, J+1 ), LDA, A( J+1, J ), 1 )
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137 CALL CSCAL( N-J, AJJ, A( J+1, J ), 1 )
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138 END IF
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139 20 CONTINUE
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140 END IF
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141 *
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142 RETURN
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143 *
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144 * End of CTRTI2
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145 *
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146 END