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annotate libcruft/lapack/strtrs.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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1 SUBROUTINE STRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB,
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2 $ INFO )
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3 *
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4 * -- LAPACK routine (version 3.1) --
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5 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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6 * November 2006
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7 *
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8 * .. Scalar Arguments ..
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9 CHARACTER DIAG, TRANS, UPLO
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10 INTEGER INFO, LDA, LDB, N, NRHS
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11 * ..
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12 * .. Array Arguments ..
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13 REAL A( LDA, * ), B( LDB, * )
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14 * ..
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15 *
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16 * Purpose
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17 * =======
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18 *
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19 * STRTRS solves a triangular system of the form
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20 *
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21 * A * X = B or A**T * X = B,
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22 *
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23 * where A is a triangular matrix of order N, and B is an N-by-NRHS
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24 * matrix. A check is made to verify that A is nonsingular.
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25 *
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26 * Arguments
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27 * =========
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28 *
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29 * UPLO (input) CHARACTER*1
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30 * = 'U': A is upper triangular;
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31 * = 'L': A is lower triangular.
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32 *
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33 * TRANS (input) CHARACTER*1
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34 * Specifies the form of the system of equations:
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35 * = 'N': A * X = B (No transpose)
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36 * = 'T': A**T * X = B (Transpose)
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37 * = 'C': A**H * X = B (Conjugate transpose = Transpose)
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38 *
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39 * DIAG (input) CHARACTER*1
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40 * = 'N': A is non-unit triangular;
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41 * = 'U': A is unit triangular.
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42 *
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43 * N (input) INTEGER
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44 * The order of the matrix A. N >= 0.
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45 *
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46 * NRHS (input) INTEGER
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47 * The number of right hand sides, i.e., the number of columns
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48 * of the matrix B. NRHS >= 0.
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49 *
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50 * A (input) REAL array, dimension (LDA,N)
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51 * The triangular matrix A. If UPLO = 'U', the leading N-by-N
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52 * upper triangular part of the array A contains the upper
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53 * triangular matrix, and the strictly lower triangular part of
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54 * A is not referenced. If UPLO = 'L', the leading N-by-N lower
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55 * triangular part of the array A contains the lower triangular
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56 * matrix, and the strictly upper triangular part of A is not
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57 * referenced. If DIAG = 'U', the diagonal elements of A are
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58 * also not referenced and are assumed to be 1.
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59 *
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60 * LDA (input) INTEGER
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61 * The leading dimension of the array A. LDA >= max(1,N).
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62 *
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63 * B (input/output) REAL array, dimension (LDB,NRHS)
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64 * On entry, the right hand side matrix B.
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65 * On exit, if INFO = 0, the solution matrix X.
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66 *
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67 * LDB (input) INTEGER
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68 * The leading dimension of the array B. LDB >= max(1,N).
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69 *
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70 * INFO (output) INTEGER
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71 * = 0: successful exit
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72 * < 0: if INFO = -i, the i-th argument had an illegal value
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73 * > 0: if INFO = i, the i-th diagonal element of A is zero,
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74 * indicating that the matrix is singular and the solutions
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75 * X have not been computed.
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76 *
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77 * =====================================================================
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78 *
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79 * .. Parameters ..
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80 REAL ZERO, ONE
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81 PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
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82 * ..
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83 * .. Local Scalars ..
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84 LOGICAL NOUNIT
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85 * ..
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86 * .. External Functions ..
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87 LOGICAL LSAME
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88 EXTERNAL LSAME
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89 * ..
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90 * .. External Subroutines ..
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91 EXTERNAL STRSM, XERBLA
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92 * ..
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93 * .. Intrinsic Functions ..
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94 INTRINSIC MAX
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95 * ..
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96 * .. Executable Statements ..
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97 *
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98 * Test the input parameters.
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99 *
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100 INFO = 0
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101 NOUNIT = LSAME( DIAG, 'N' )
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102 IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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103 INFO = -1
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104 ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
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105 $ LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
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106 INFO = -2
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107 ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
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108 INFO = -3
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109 ELSE IF( N.LT.0 ) THEN
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110 INFO = -4
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111 ELSE IF( NRHS.LT.0 ) THEN
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112 INFO = -5
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113 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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114 INFO = -7
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115 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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116 INFO = -9
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117 END IF
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118 IF( INFO.NE.0 ) THEN
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119 CALL XERBLA( 'STRTRS', -INFO )
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120 RETURN
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121 END IF
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122 *
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123 * Quick return if possible
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124 *
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125 IF( N.EQ.0 )
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126 $ RETURN
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127 *
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128 * Check for singularity.
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129 *
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130 IF( NOUNIT ) THEN
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131 DO 10 INFO = 1, N
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132 IF( A( INFO, INFO ).EQ.ZERO )
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133 $ RETURN
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134 10 CONTINUE
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135 END IF
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136 INFO = 0
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137 *
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138 * Solve A * x = b or A' * x = b.
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139 *
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140 CALL STRSM( 'Left', UPLO, TRANS, DIAG, N, NRHS, ONE, A, LDA, B,
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141 $ LDB )
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142 *
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143 RETURN
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144 *
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145 * End of STRTRS
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146 *
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147 END