| 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 |
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