1DSYR2(1)                         BLAS routine                         DSYR2(1)
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NAME

6       DSYR2 - the symmetric rank 2 operation   A := alpha*x*y' + alpha*y*x' +
7       A,
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SYNOPSIS

10       SUBROUTINE DSYR2(UPLO,N,ALPHA,X,INCX,Y,INCY,A,LDA)
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12           DOUBLE                                         PRECISION ALPHA
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14           INTEGER                                        INCX,INCY,LDA,N
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16           CHARACTER                                      UPLO
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18           DOUBLE                                         PRECISION
19                                                          A(LDA,*),X(*),Y(*)
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PURPOSE

22       DSYR2  performs the symmetric rank 2 operation
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24       where alpha is a scalar, x and y are n element vectors and A is an n by
25       n symmetric matrix.
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ARGUMENTS

29       UPLO   - CHARACTER*1.
30              On entry, UPLO specifies whether the upper or  lower  triangular
31              part of the array A is to be referenced as follows:
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33              UPLO = 'U' or 'u'   Only the upper triangular part of A is to be
34              referenced.
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36              UPLO = 'L' or 'l'   Only the lower triangular part of A is to be
37              referenced.
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39              Unchanged on exit.
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41       N      - INTEGER.
42              On  entry,  N specifies the order of the matrix A.  N must be at
43              least zero.  Unchanged on exit.
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45       ALPHA  - DOUBLE PRECISION.
46              On entry, ALPHA specifies the scalar alpha.  Unchanged on exit.
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48       X      - DOUBLE PRECISION array of dimension at least
49              ( 1 + ( n - 1 )*abs( INCX ) ).  Before  entry,  the  incremented
50              array X must contain the n element vector x.  Unchanged on exit.
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52       INCX   - INTEGER.
53              On  entry,  INCX  specifies the increment for the elements of X.
54              INCX must not be zero.  Unchanged on exit.
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56       Y      - DOUBLE PRECISION array of dimension at least
57              ( 1 + ( n - 1 )*abs( INCY ) ).  Before  entry,  the  incremented
58              array Y must contain the n element vector y.  Unchanged on exit.
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60       INCY   - INTEGER.
61              On  entry,  INCY  specifies the increment for the elements of Y.
62              INCY must not be zero.  Unchanged on exit.
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64       A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
65              Before entry with  UPLO = 'U' or 'u', the leading n by  n  upper
66              triangular part of the array A must contain the upper triangular
67              part of the symmetric matrix and the strictly  lower  triangular
68              part  of A is not referenced. On exit, the upper triangular part
69              of the array A is overwritten by the upper  triangular  part  of
70              the  updated  matrix.   Before entry with UPLO = 'L' or 'l', the
71              leading n by n lower triangular part of the array A must contain
72              the  lower  triangular  part  of  the  symmetric  matrix and the
73              strictly upper triangular part of A is not referenced. On  exit,
74              the  lower  triangular part of the array A is overwritten by the
75              lower triangular part of the updated matrix.
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77       LDA    - INTEGER.
78              On entry, LDA specifies the first dimension of A as declared  in
79              the  calling  (sub)  program.  LDA must be at least max( 1, n ).
80              Unchanged on exit.
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82              Level 2 Blas routine.
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84              -- Written on 22-October-1986.  Jack Dongarra, Argonne  National
85              Lab.   Jeremy Du Croz, Nag Central Office.  Sven Hammarling, Nag
86              Central Office.  Richard Hanson, Sandia National Labs.
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90BLAS routine                     November 2006                        DSYR2(1)