1 | *> \brief \b SLARZB |
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2 | * |
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3 | * =========== DOCUMENTATION =========== |
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4 | * |
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5 | * Online html documentation available at |
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6 | * http://www.netlib.org/lapack/explore-html/ |
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7 | * |
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8 | *> \htmlonly |
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9 | *> Download SLARZB + dependencies |
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10 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slarzb.f"> |
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11 | *> [TGZ]</a> |
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12 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slarzb.f"> |
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13 | *> [ZIP]</a> |
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14 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slarzb.f"> |
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15 | *> [TXT]</a> |
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16 | *> \endhtmlonly |
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17 | * |
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18 | * Definition: |
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19 | * =========== |
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20 | * |
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21 | * SUBROUTINE SLARZB( SIDE, TRANS, DIRECT, STOREV, M, N, K, L, V, |
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22 | * LDV, T, LDT, C, LDC, WORK, LDWORK ) |
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23 | * |
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24 | * .. Scalar Arguments .. |
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25 | * CHARACTER DIRECT, SIDE, STOREV, TRANS |
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26 | * INTEGER K, L, LDC, LDT, LDV, LDWORK, M, N |
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27 | * .. |
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28 | * .. Array Arguments .. |
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29 | * REAL C( LDC, * ), T( LDT, * ), V( LDV, * ), |
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30 | * $ WORK( LDWORK, * ) |
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31 | * .. |
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32 | * |
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33 | * |
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34 | *> \par Purpose: |
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35 | * ============= |
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36 | *> |
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37 | *> \verbatim |
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38 | *> |
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39 | *> SLARZB applies a real block reflector H or its transpose H**T to |
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40 | *> a real distributed M-by-N C from the left or the right. |
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41 | *> |
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42 | *> Currently, only STOREV = 'R' and DIRECT = 'B' are supported. |
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43 | *> \endverbatim |
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44 | * |
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45 | * Arguments: |
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46 | * ========== |
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47 | * |
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48 | *> \param[in] SIDE |
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49 | *> \verbatim |
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50 | *> SIDE is CHARACTER*1 |
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51 | *> = 'L': apply H or H**T from the Left |
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52 | *> = 'R': apply H or H**T from the Right |
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53 | *> \endverbatim |
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54 | *> |
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55 | *> \param[in] TRANS |
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56 | *> \verbatim |
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57 | *> TRANS is CHARACTER*1 |
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58 | *> = 'N': apply H (No transpose) |
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59 | *> = 'C': apply H**T (Transpose) |
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60 | *> \endverbatim |
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61 | *> |
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62 | *> \param[in] DIRECT |
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63 | *> \verbatim |
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64 | *> DIRECT is CHARACTER*1 |
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65 | *> Indicates how H is formed from a product of elementary |
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66 | *> reflectors |
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67 | *> = 'F': H = H(1) H(2) . . . H(k) (Forward, not supported yet) |
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68 | *> = 'B': H = H(k) . . . H(2) H(1) (Backward) |
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69 | *> \endverbatim |
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70 | *> |
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71 | *> \param[in] STOREV |
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72 | *> \verbatim |
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73 | *> STOREV is CHARACTER*1 |
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74 | *> Indicates how the vectors which define the elementary |
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75 | *> reflectors are stored: |
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76 | *> = 'C': Columnwise (not supported yet) |
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77 | *> = 'R': Rowwise |
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78 | *> \endverbatim |
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79 | *> |
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80 | *> \param[in] M |
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81 | *> \verbatim |
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82 | *> M is INTEGER |
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83 | *> The number of rows of the matrix C. |
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84 | *> \endverbatim |
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85 | *> |
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86 | *> \param[in] N |
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87 | *> \verbatim |
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88 | *> N is INTEGER |
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89 | *> The number of columns of the matrix C. |
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90 | *> \endverbatim |
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91 | *> |
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92 | *> \param[in] K |
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93 | *> \verbatim |
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94 | *> K is INTEGER |
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95 | *> The order of the matrix T (= the number of elementary |
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96 | *> reflectors whose product defines the block reflector). |
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97 | *> \endverbatim |
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98 | *> |
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99 | *> \param[in] L |
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100 | *> \verbatim |
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101 | *> L is INTEGER |
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102 | *> The number of columns of the matrix V containing the |
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103 | *> meaningful part of the Householder reflectors. |
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104 | *> If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0. |
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105 | *> \endverbatim |
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106 | *> |
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107 | *> \param[in] V |
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108 | *> \verbatim |
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109 | *> V is REAL array, dimension (LDV,NV). |
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110 | *> If STOREV = 'C', NV = K; if STOREV = 'R', NV = L. |
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111 | *> \endverbatim |
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112 | *> |
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113 | *> \param[in] LDV |
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114 | *> \verbatim |
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115 | *> LDV is INTEGER |
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116 | *> The leading dimension of the array V. |
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117 | *> If STOREV = 'C', LDV >= L; if STOREV = 'R', LDV >= K. |
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118 | *> \endverbatim |
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119 | *> |
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120 | *> \param[in] T |
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121 | *> \verbatim |
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122 | *> T is REAL array, dimension (LDT,K) |
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123 | *> The triangular K-by-K matrix T in the representation of the |
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124 | *> block reflector. |
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125 | *> \endverbatim |
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126 | *> |
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127 | *> \param[in] LDT |
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128 | *> \verbatim |
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129 | *> LDT is INTEGER |
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130 | *> The leading dimension of the array T. LDT >= K. |
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131 | *> \endverbatim |
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132 | *> |
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133 | *> \param[in,out] C |
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134 | *> \verbatim |
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135 | *> C is REAL array, dimension (LDC,N) |
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136 | *> On entry, the M-by-N matrix C. |
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137 | *> On exit, C is overwritten by H*C or H**T*C or C*H or C*H**T. |
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138 | *> \endverbatim |
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139 | *> |
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140 | *> \param[in] LDC |
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141 | *> \verbatim |
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142 | *> LDC is INTEGER |
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143 | *> The leading dimension of the array C. LDC >= max(1,M). |
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144 | *> \endverbatim |
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145 | *> |
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146 | *> \param[out] WORK |
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147 | *> \verbatim |
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148 | *> WORK is REAL array, dimension (LDWORK,K) |
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149 | *> \endverbatim |
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150 | *> |
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151 | *> \param[in] LDWORK |
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152 | *> \verbatim |
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153 | *> LDWORK is INTEGER |
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154 | *> The leading dimension of the array WORK. |
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155 | *> If SIDE = 'L', LDWORK >= max(1,N); |
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156 | *> if SIDE = 'R', LDWORK >= max(1,M). |
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157 | *> \endverbatim |
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158 | * |
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159 | * Authors: |
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160 | * ======== |
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161 | * |
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162 | *> \author Univ. of Tennessee |
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163 | *> \author Univ. of California Berkeley |
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164 | *> \author Univ. of Colorado Denver |
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165 | *> \author NAG Ltd. |
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166 | * |
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167 | *> \date November 2011 |
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168 | * |
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169 | *> \ingroup realOTHERcomputational |
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170 | * |
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171 | *> \par Contributors: |
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172 | * ================== |
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173 | *> |
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174 | *> A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA |
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175 | * |
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176 | *> \par Further Details: |
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177 | * ===================== |
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178 | *> |
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179 | *> \verbatim |
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180 | *> \endverbatim |
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181 | *> |
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182 | * ===================================================================== |
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183 | SUBROUTINE SLARZB( SIDE, TRANS, DIRECT, STOREV, M, N, K, L, V, |
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184 | $ LDV, T, LDT, C, LDC, WORK, LDWORK ) |
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185 | * |
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186 | * -- LAPACK computational routine (version 3.4.0) -- |
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187 | * -- LAPACK is a software package provided by Univ. of Tennessee, -- |
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188 | * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
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189 | * November 2011 |
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190 | * |
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191 | * .. Scalar Arguments .. |
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192 | CHARACTER DIRECT, SIDE, STOREV, TRANS |
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193 | INTEGER K, L, LDC, LDT, LDV, LDWORK, M, N |
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194 | * .. |
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195 | * .. Array Arguments .. |
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196 | REAL C( LDC, * ), T( LDT, * ), V( LDV, * ), |
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197 | $ WORK( LDWORK, * ) |
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198 | * .. |
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199 | * |
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200 | * ===================================================================== |
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201 | * |
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202 | * .. Parameters .. |
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203 | REAL ONE |
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204 | PARAMETER ( ONE = 1.0E+0 ) |
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205 | * .. |
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206 | * .. Local Scalars .. |
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207 | CHARACTER TRANST |
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208 | INTEGER I, INFO, J |
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209 | * .. |
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210 | * .. External Functions .. |
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211 | LOGICAL LSAME |
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212 | EXTERNAL LSAME |
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213 | * .. |
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214 | * .. External Subroutines .. |
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215 | EXTERNAL SCOPY, SGEMM, STRMM, XERBLA |
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216 | * .. |
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217 | * .. Executable Statements .. |
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218 | * |
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219 | * Quick return if possible |
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220 | * |
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221 | IF( M.LE.0 .OR. N.LE.0 ) |
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222 | $ RETURN |
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223 | * |
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224 | * Check for currently supported options |
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225 | * |
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226 | INFO = 0 |
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227 | IF( .NOT.LSAME( DIRECT, 'B' ) ) THEN |
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228 | INFO = -3 |
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229 | ELSE IF( .NOT.LSAME( STOREV, 'R' ) ) THEN |
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230 | INFO = -4 |
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231 | END IF |
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232 | IF( INFO.NE.0 ) THEN |
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233 | CALL XERBLA( 'SLARZB', -INFO ) |
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234 | RETURN |
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235 | END IF |
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236 | * |
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237 | IF( LSAME( TRANS, 'N' ) ) THEN |
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238 | TRANST = 'T' |
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239 | ELSE |
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240 | TRANST = 'N' |
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241 | END IF |
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242 | * |
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243 | IF( LSAME( SIDE, 'L' ) ) THEN |
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244 | * |
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245 | * Form H * C or H**T * C |
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246 | * |
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247 | * W( 1:n, 1:k ) = C( 1:k, 1:n )**T |
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248 | * |
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249 | DO 10 J = 1, K |
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250 | CALL SCOPY( N, C( J, 1 ), LDC, WORK( 1, J ), 1 ) |
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251 | 10 CONTINUE |
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252 | * |
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253 | * W( 1:n, 1:k ) = W( 1:n, 1:k ) + ... |
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254 | * C( m-l+1:m, 1:n )**T * V( 1:k, 1:l )**T |
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255 | * |
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256 | IF( L.GT.0 ) |
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257 | $ CALL SGEMM( 'Transpose', 'Transpose', N, K, L, ONE, |
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258 | $ C( M-L+1, 1 ), LDC, V, LDV, ONE, WORK, LDWORK ) |
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259 | * |
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260 | * W( 1:n, 1:k ) = W( 1:n, 1:k ) * T**T or W( 1:m, 1:k ) * T |
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261 | * |
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262 | CALL STRMM( 'Right', 'Lower', TRANST, 'Non-unit', N, K, ONE, T, |
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263 | $ LDT, WORK, LDWORK ) |
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264 | * |
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265 | * C( 1:k, 1:n ) = C( 1:k, 1:n ) - W( 1:n, 1:k )**T |
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266 | * |
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267 | DO 30 J = 1, N |
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268 | DO 20 I = 1, K |
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269 | C( I, J ) = C( I, J ) - WORK( J, I ) |
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270 | 20 CONTINUE |
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271 | 30 CONTINUE |
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272 | * |
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273 | * C( m-l+1:m, 1:n ) = C( m-l+1:m, 1:n ) - ... |
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274 | * V( 1:k, 1:l )**T * W( 1:n, 1:k )**T |
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275 | * |
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276 | IF( L.GT.0 ) |
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277 | $ CALL SGEMM( 'Transpose', 'Transpose', L, N, K, -ONE, V, LDV, |
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278 | $ WORK, LDWORK, ONE, C( M-L+1, 1 ), LDC ) |
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279 | * |
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280 | ELSE IF( LSAME( SIDE, 'R' ) ) THEN |
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281 | * |
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282 | * Form C * H or C * H**T |
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283 | * |
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284 | * W( 1:m, 1:k ) = C( 1:m, 1:k ) |
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285 | * |
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286 | DO 40 J = 1, K |
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287 | CALL SCOPY( M, C( 1, J ), 1, WORK( 1, J ), 1 ) |
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288 | 40 CONTINUE |
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289 | * |
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290 | * W( 1:m, 1:k ) = W( 1:m, 1:k ) + ... |
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291 | * C( 1:m, n-l+1:n ) * V( 1:k, 1:l )**T |
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292 | * |
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293 | IF( L.GT.0 ) |
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294 | $ CALL SGEMM( 'No transpose', 'Transpose', M, K, L, ONE, |
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295 | $ C( 1, N-L+1 ), LDC, V, LDV, ONE, WORK, LDWORK ) |
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296 | * |
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297 | * W( 1:m, 1:k ) = W( 1:m, 1:k ) * T or W( 1:m, 1:k ) * T**T |
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298 | * |
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299 | CALL STRMM( 'Right', 'Lower', TRANS, 'Non-unit', M, K, ONE, T, |
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300 | $ LDT, WORK, LDWORK ) |
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301 | * |
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302 | * C( 1:m, 1:k ) = C( 1:m, 1:k ) - W( 1:m, 1:k ) |
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303 | * |
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304 | DO 60 J = 1, K |
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305 | DO 50 I = 1, M |
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306 | C( I, J ) = C( I, J ) - WORK( I, J ) |
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307 | 50 CONTINUE |
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308 | 60 CONTINUE |
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309 | * |
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310 | * C( 1:m, n-l+1:n ) = C( 1:m, n-l+1:n ) - ... |
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311 | * W( 1:m, 1:k ) * V( 1:k, 1:l ) |
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312 | * |
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313 | IF( L.GT.0 ) |
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314 | $ CALL SGEMM( 'No transpose', 'No transpose', M, L, K, -ONE, |
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315 | $ WORK, LDWORK, V, LDV, ONE, C( 1, N-L+1 ), LDC ) |
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316 | * |
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317 | END IF |
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318 | * |
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319 | RETURN |
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320 | * |
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321 | * End of SLARZB |
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322 | * |
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323 | END |
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