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1 SUBROUTINE SPOTF2( UPLO, N, A, LDA, INFO ) |
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2 * |
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7034
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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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4329
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6 * |
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7 * .. Scalar Arguments .. |
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8 CHARACTER 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 REAL 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 * SPOTF2 computes the Cholesky factorization of a real symmetric |
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19 * positive definite matrix A. |
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20 * |
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21 * The factorization has the form |
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22 * A = U' * U , if UPLO = 'U', or |
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23 * A = L * L', if UPLO = 'L', |
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24 * where U is an upper triangular matrix and L is lower triangular. |
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25 * |
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26 * This is the unblocked version of the algorithm, calling Level 2 BLAS. |
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27 * |
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28 * Arguments |
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29 * ========= |
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30 * |
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31 * UPLO (input) CHARACTER*1 |
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32 * Specifies whether the upper or lower triangular part of the |
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33 * symmetric matrix A is stored. |
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34 * = 'U': Upper triangular |
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35 * = 'L': Lower triangular |
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36 * |
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37 * N (input) INTEGER |
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38 * The order of the matrix A. N >= 0. |
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39 * |
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40 * A (input/output) REAL array, dimension (LDA,N) |
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41 * On entry, the symmetric matrix A. If UPLO = 'U', the leading |
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42 * n by n upper triangular part of A contains the upper |
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43 * triangular part of the matrix A, and the strictly lower |
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44 * triangular part of A is not referenced. If UPLO = 'L', the |
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45 * leading n by n lower triangular part of A contains the lower |
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46 * triangular part of the matrix A, and the strictly upper |
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47 * triangular part of A is not referenced. |
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48 * |
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49 * On exit, if INFO = 0, the factor U or L from the Cholesky |
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50 * factorization A = U'*U or A = L*L'. |
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51 * |
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52 * LDA (input) INTEGER |
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53 * The leading dimension of the array A. LDA >= max(1,N). |
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54 * |
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55 * INFO (output) INTEGER |
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56 * = 0: successful exit |
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57 * < 0: if INFO = -k, the k-th argument had an illegal value |
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58 * > 0: if INFO = k, the leading minor of order k is not |
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59 * positive definite, and the factorization could not be |
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60 * completed. |
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61 * |
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62 * ===================================================================== |
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63 * |
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64 * .. Parameters .. |
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65 REAL ONE, ZERO |
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66 PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) |
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67 * .. |
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68 * .. Local Scalars .. |
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69 LOGICAL UPPER |
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70 INTEGER J |
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71 REAL AJJ |
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72 * .. |
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73 * .. External Functions .. |
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74 LOGICAL LSAME |
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75 REAL SDOT |
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76 EXTERNAL LSAME, SDOT |
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77 * .. |
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78 * .. External Subroutines .. |
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79 EXTERNAL SGEMV, SSCAL, XERBLA |
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80 * .. |
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81 * .. Intrinsic Functions .. |
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82 INTRINSIC MAX, SQRT |
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83 * .. |
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84 * .. Executable Statements .. |
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85 * |
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86 * Test the input parameters. |
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87 * |
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88 INFO = 0 |
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89 UPPER = LSAME( UPLO, 'U' ) |
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90 IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN |
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91 INFO = -1 |
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92 ELSE IF( N.LT.0 ) THEN |
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93 INFO = -2 |
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94 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN |
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95 INFO = -4 |
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96 END IF |
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97 IF( INFO.NE.0 ) THEN |
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98 CALL XERBLA( 'SPOTF2', -INFO ) |
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99 RETURN |
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100 END IF |
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101 * |
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102 * Quick return if possible |
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103 * |
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104 IF( N.EQ.0 ) |
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105 $ RETURN |
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106 * |
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107 IF( UPPER ) THEN |
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108 * |
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109 * Compute the Cholesky factorization A = U'*U. |
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110 * |
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111 DO 10 J = 1, N |
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112 * |
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113 * Compute U(J,J) and test for non-positive-definiteness. |
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114 * |
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115 AJJ = A( J, J ) - SDOT( J-1, A( 1, J ), 1, A( 1, J ), 1 ) |
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116 IF( AJJ.LE.ZERO ) THEN |
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117 A( J, J ) = AJJ |
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118 GO TO 30 |
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119 END IF |
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120 AJJ = SQRT( AJJ ) |
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121 A( J, J ) = AJJ |
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122 * |
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123 * Compute elements J+1:N of row J. |
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124 * |
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125 IF( J.LT.N ) THEN |
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126 CALL SGEMV( 'Transpose', J-1, N-J, -ONE, A( 1, J+1 ), |
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127 $ LDA, A( 1, J ), 1, ONE, A( J, J+1 ), LDA ) |
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128 CALL SSCAL( N-J, ONE / AJJ, A( J, J+1 ), LDA ) |
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129 END IF |
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130 10 CONTINUE |
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131 ELSE |
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132 * |
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133 * Compute the Cholesky factorization A = L*L'. |
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134 * |
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135 DO 20 J = 1, N |
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136 * |
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137 * Compute L(J,J) and test for non-positive-definiteness. |
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138 * |
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139 AJJ = A( J, J ) - SDOT( J-1, A( J, 1 ), LDA, A( J, 1 ), |
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140 $ LDA ) |
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141 IF( AJJ.LE.ZERO ) THEN |
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142 A( J, J ) = AJJ |
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143 GO TO 30 |
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144 END IF |
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145 AJJ = SQRT( AJJ ) |
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146 A( J, J ) = AJJ |
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147 * |
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148 * Compute elements J+1:N of column J. |
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149 * |
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150 IF( J.LT.N ) THEN |
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151 CALL SGEMV( 'No transpose', N-J, J-1, -ONE, A( J+1, 1 ), |
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152 $ LDA, A( J, 1 ), LDA, ONE, A( J+1, J ), 1 ) |
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153 CALL SSCAL( N-J, ONE / AJJ, A( J+1, J ), 1 ) |
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154 END IF |
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155 20 CONTINUE |
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156 END IF |
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157 GO TO 40 |
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158 * |
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159 30 CONTINUE |
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160 INFO = J |
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161 * |
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162 40 CONTINUE |
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163 RETURN |
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164 * |
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165 * End of SPOTF2 |
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166 * |
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167 END |
