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annotate libcruft/blas/ssyr2.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 SSYR2(UPLO,N,ALPHA,X,INCX,Y,INCY,A,LDA)
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2 * .. Scalar Arguments ..
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3 REAL ALPHA
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4 INTEGER INCX,INCY,LDA,N
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5 CHARACTER UPLO
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6 * ..
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7 * .. Array Arguments ..
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8 REAL A(LDA,*),X(*),Y(*)
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9 * ..
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10 *
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11 * Purpose
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12 * =======
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13 *
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14 * SSYR2 performs the symmetric rank 2 operation
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15 *
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16 * A := alpha*x*y' + alpha*y*x' + A,
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17 *
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18 * where alpha is a scalar, x and y are n element vectors and A is an n
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19 * by n symmetric matrix.
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20 *
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21 * Arguments
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22 * ==========
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23 *
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24 * UPLO - CHARACTER*1.
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25 * On entry, UPLO specifies whether the upper or lower
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26 * triangular part of the array A is to be referenced as
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27 * follows:
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28 *
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29 * UPLO = 'U' or 'u' Only the upper triangular part of A
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30 * is to be referenced.
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31 *
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32 * UPLO = 'L' or 'l' Only the lower triangular part of A
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33 * is to be referenced.
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34 *
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35 * Unchanged on exit.
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36 *
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37 * N - INTEGER.
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38 * On entry, N specifies the order of the matrix A.
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39 * N must be at least zero.
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40 * Unchanged on exit.
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41 *
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42 * ALPHA - REAL .
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43 * On entry, ALPHA specifies the scalar alpha.
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44 * Unchanged on exit.
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45 *
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46 * X - REAL array of dimension at least
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47 * ( 1 + ( n - 1 )*abs( INCX ) ).
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48 * Before entry, the incremented array X must contain the n
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49 * element vector x.
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50 * Unchanged on exit.
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51 *
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52 * INCX - INTEGER.
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53 * On entry, INCX specifies the increment for the elements of
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54 * X. INCX must not be zero.
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55 * Unchanged on exit.
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56 *
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57 * Y - REAL array of dimension at least
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58 * ( 1 + ( n - 1 )*abs( INCY ) ).
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59 * Before entry, the incremented array Y must contain the n
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60 * element vector y.
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61 * Unchanged on exit.
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62 *
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63 * INCY - INTEGER.
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64 * On entry, INCY specifies the increment for the elements of
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65 * Y. INCY must not be zero.
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66 * Unchanged on exit.
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67 *
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68 * A - REAL array of DIMENSION ( LDA, n ).
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69 * Before entry with UPLO = 'U' or 'u', the leading n by n
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70 * upper triangular part of the array A must contain the upper
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71 * triangular part of the symmetric matrix and the strictly
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72 * lower triangular part of A is not referenced. On exit, the
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73 * upper triangular part of the array A is overwritten by the
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74 * upper triangular part of the updated matrix.
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75 * Before entry with UPLO = 'L' or 'l', the leading n by n
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76 * lower triangular part of the array A must contain the lower
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77 * triangular part of the symmetric matrix and the strictly
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78 * upper triangular part of A is not referenced. On exit, the
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79 * lower triangular part of the array A is overwritten by the
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80 * lower triangular part of the updated matrix.
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81 *
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82 * LDA - INTEGER.
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83 * On entry, LDA specifies the first dimension of A as declared
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84 * in the calling (sub) program. LDA must be at least
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85 * max( 1, n ).
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86 * Unchanged on exit.
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87 *
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88 *
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89 * Level 2 Blas routine.
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90 *
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91 * -- Written on 22-October-1986.
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92 * Jack Dongarra, Argonne National Lab.
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93 * Jeremy Du Croz, Nag Central Office.
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94 * Sven Hammarling, Nag Central Office.
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95 * Richard Hanson, Sandia National Labs.
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96 *
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97 *
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98 * .. Parameters ..
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99 REAL ZERO
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100 PARAMETER (ZERO=0.0E+0)
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101 * ..
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102 * .. Local Scalars ..
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103 REAL TEMP1,TEMP2
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104 INTEGER I,INFO,IX,IY,J,JX,JY,KX,KY
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105 * ..
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106 * .. External Functions ..
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107 LOGICAL LSAME
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108 EXTERNAL LSAME
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109 * ..
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110 * .. External Subroutines ..
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111 EXTERNAL XERBLA
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112 * ..
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113 * .. Intrinsic Functions ..
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114 INTRINSIC MAX
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115 * ..
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116 *
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117 * Test the input parameters.
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118 *
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119 INFO = 0
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120 IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
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121 INFO = 1
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122 ELSE IF (N.LT.0) THEN
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123 INFO = 2
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124 ELSE IF (INCX.EQ.0) THEN
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125 INFO = 5
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126 ELSE IF (INCY.EQ.0) THEN
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127 INFO = 7
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128 ELSE IF (LDA.LT.MAX(1,N)) THEN
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129 INFO = 9
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130 END IF
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131 IF (INFO.NE.0) THEN
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132 CALL XERBLA('SSYR2 ',INFO)
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133 RETURN
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134 END IF
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135 *
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136 * Quick return if possible.
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137 *
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138 IF ((N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
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139 *
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140 * Set up the start points in X and Y if the increments are not both
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141 * unity.
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142 *
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143 IF ((INCX.NE.1) .OR. (INCY.NE.1)) THEN
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144 IF (INCX.GT.0) THEN
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145 KX = 1
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146 ELSE
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147 KX = 1 - (N-1)*INCX
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148 END IF
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149 IF (INCY.GT.0) THEN
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150 KY = 1
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151 ELSE
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152 KY = 1 - (N-1)*INCY
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153 END IF
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154 JX = KX
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155 JY = KY
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156 END IF
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157 *
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158 * Start the operations. In this version the elements of A are
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159 * accessed sequentially with one pass through the triangular part
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160 * of A.
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161 *
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162 IF (LSAME(UPLO,'U')) THEN
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163 *
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164 * Form A when A is stored in the upper triangle.
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165 *
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166 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
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167 DO 20 J = 1,N
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168 IF ((X(J).NE.ZERO) .OR. (Y(J).NE.ZERO)) THEN
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169 TEMP1 = ALPHA*Y(J)
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170 TEMP2 = ALPHA*X(J)
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171 DO 10 I = 1,J
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172 A(I,J) = A(I,J) + X(I)*TEMP1 + Y(I)*TEMP2
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173 10 CONTINUE
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174 END IF
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175 20 CONTINUE
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176 ELSE
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177 DO 40 J = 1,N
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178 IF ((X(JX).NE.ZERO) .OR. (Y(JY).NE.ZERO)) THEN
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179 TEMP1 = ALPHA*Y(JY)
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180 TEMP2 = ALPHA*X(JX)
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181 IX = KX
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182 IY = KY
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183 DO 30 I = 1,J
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184 A(I,J) = A(I,J) + X(IX)*TEMP1 + Y(IY)*TEMP2
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185 IX = IX + INCX
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186 IY = IY + INCY
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187 30 CONTINUE
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188 END IF
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189 JX = JX + INCX
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190 JY = JY + INCY
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191 40 CONTINUE
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192 END IF
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193 ELSE
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194 *
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195 * Form A when A is stored in the lower triangle.
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196 *
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197 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
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198 DO 60 J = 1,N
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199 IF ((X(J).NE.ZERO) .OR. (Y(J).NE.ZERO)) THEN
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200 TEMP1 = ALPHA*Y(J)
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201 TEMP2 = ALPHA*X(J)
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202 DO 50 I = J,N
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203 A(I,J) = A(I,J) + X(I)*TEMP1 + Y(I)*TEMP2
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204 50 CONTINUE
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205 END IF
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206 60 CONTINUE
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207 ELSE
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208 DO 80 J = 1,N
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209 IF ((X(JX).NE.ZERO) .OR. (Y(JY).NE.ZERO)) THEN
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210 TEMP1 = ALPHA*Y(JY)
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211 TEMP2 = ALPHA*X(JX)
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212 IX = JX
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213 IY = JY
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214 DO 70 I = J,N
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215 A(I,J) = A(I,J) + X(IX)*TEMP1 + Y(IY)*TEMP2
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216 IX = IX + INCX
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217 IY = IY + INCY
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218 70 CONTINUE
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219 END IF
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220 JX = JX + INCX
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221 JY = JY + INCY
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222 80 CONTINUE
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223 END IF
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224 END IF
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225 *
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226 RETURN
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227 *
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228 * End of SSYR2 .
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229 *
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230 END