Annotation of rpl/lapack/blas/dsyr.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DSYR(UPLO,N,ALPHA,X,INCX,A,LDA)
! 2: * .. Scalar Arguments ..
! 3: DOUBLE PRECISION ALPHA
! 4: INTEGER INCX,LDA,N
! 5: CHARACTER UPLO
! 6: * ..
! 7: * .. Array Arguments ..
! 8: DOUBLE PRECISION A(LDA,*),X(*)
! 9: * ..
! 10: *
! 11: * Purpose
! 12: * =======
! 13: *
! 14: * DSYR 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 - DOUBLE PRECISION.
! 43: * On entry, ALPHA specifies the scalar alpha.
! 44: * Unchanged on exit.
! 45: *
! 46: * X - DOUBLE PRECISION 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 - DOUBLE PRECISION 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: * Further Details
! 78: * ===============
! 79: *
! 80: * Level 2 Blas routine.
! 81: *
! 82: * -- Written on 22-October-1986.
! 83: * Jack Dongarra, Argonne National Lab.
! 84: * Jeremy Du Croz, Nag Central Office.
! 85: * Sven Hammarling, Nag Central Office.
! 86: * Richard Hanson, Sandia National Labs.
! 87: *
! 88: * =====================================================================
! 89: *
! 90: * .. Parameters ..
! 91: DOUBLE PRECISION ZERO
! 92: PARAMETER (ZERO=0.0D+0)
! 93: * ..
! 94: * .. Local Scalars ..
! 95: DOUBLE PRECISION TEMP
! 96: INTEGER I,INFO,IX,J,JX,KX
! 97: * ..
! 98: * .. External Functions ..
! 99: LOGICAL LSAME
! 100: EXTERNAL LSAME
! 101: * ..
! 102: * .. External Subroutines ..
! 103: EXTERNAL XERBLA
! 104: * ..
! 105: * .. Intrinsic Functions ..
! 106: INTRINSIC MAX
! 107: * ..
! 108: *
! 109: * Test the input parameters.
! 110: *
! 111: INFO = 0
! 112: IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
! 113: INFO = 1
! 114: ELSE IF (N.LT.0) THEN
! 115: INFO = 2
! 116: ELSE IF (INCX.EQ.0) THEN
! 117: INFO = 5
! 118: ELSE IF (LDA.LT.MAX(1,N)) THEN
! 119: INFO = 7
! 120: END IF
! 121: IF (INFO.NE.0) THEN
! 122: CALL XERBLA('DSYR ',INFO)
! 123: RETURN
! 124: END IF
! 125: *
! 126: * Quick return if possible.
! 127: *
! 128: IF ((N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
! 129: *
! 130: * Set the start point in X if the increment is not unity.
! 131: *
! 132: IF (INCX.LE.0) THEN
! 133: KX = 1 - (N-1)*INCX
! 134: ELSE IF (INCX.NE.1) THEN
! 135: KX = 1
! 136: END IF
! 137: *
! 138: * Start the operations. In this version the elements of A are
! 139: * accessed sequentially with one pass through the triangular part
! 140: * of A.
! 141: *
! 142: IF (LSAME(UPLO,'U')) THEN
! 143: *
! 144: * Form A when A is stored in upper triangle.
! 145: *
! 146: IF (INCX.EQ.1) THEN
! 147: DO 20 J = 1,N
! 148: IF (X(J).NE.ZERO) THEN
! 149: TEMP = ALPHA*X(J)
! 150: DO 10 I = 1,J
! 151: A(I,J) = A(I,J) + X(I)*TEMP
! 152: 10 CONTINUE
! 153: END IF
! 154: 20 CONTINUE
! 155: ELSE
! 156: JX = KX
! 157: DO 40 J = 1,N
! 158: IF (X(JX).NE.ZERO) THEN
! 159: TEMP = ALPHA*X(JX)
! 160: IX = KX
! 161: DO 30 I = 1,J
! 162: A(I,J) = A(I,J) + X(IX)*TEMP
! 163: IX = IX + INCX
! 164: 30 CONTINUE
! 165: END IF
! 166: JX = JX + INCX
! 167: 40 CONTINUE
! 168: END IF
! 169: ELSE
! 170: *
! 171: * Form A when A is stored in lower triangle.
! 172: *
! 173: IF (INCX.EQ.1) THEN
! 174: DO 60 J = 1,N
! 175: IF (X(J).NE.ZERO) THEN
! 176: TEMP = ALPHA*X(J)
! 177: DO 50 I = J,N
! 178: A(I,J) = A(I,J) + X(I)*TEMP
! 179: 50 CONTINUE
! 180: END IF
! 181: 60 CONTINUE
! 182: ELSE
! 183: JX = KX
! 184: DO 80 J = 1,N
! 185: IF (X(JX).NE.ZERO) THEN
! 186: TEMP = ALPHA*X(JX)
! 187: IX = JX
! 188: DO 70 I = J,N
! 189: A(I,J) = A(I,J) + X(IX)*TEMP
! 190: IX = IX + INCX
! 191: 70 CONTINUE
! 192: END IF
! 193: JX = JX + INCX
! 194: 80 CONTINUE
! 195: END IF
! 196: END IF
! 197: *
! 198: RETURN
! 199: *
! 200: * End of DSYR .
! 201: *
! 202: END
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