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