1SSYR2(1)                         BLAS routine                         SSYR2(1)
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NAME

6       SSYR2  -  performs  the  symmetric rank 2 operation   A := alpha*x*y' +
7       alpha*y*x' + A,
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SYNOPSIS

10       SUBROUTINE SSYR2(UPLO,N,ALPHA,X,INCX,Y,INCY,A,LDA)
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12           REAL                                           ALPHA
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14           INTEGER                                        INCX,INCY,LDA,N
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16           CHARACTER                                      UPLO
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18           REAL                                           A(LDA,*),X(*),Y(*)
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PURPOSE

21       SSYR2  performs the symmetric rank 2 operation
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23       where alpha is a scalar, x and y are n element vectors and A is an n by
24       n symmetric matrix.
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ARGUMENTS

28       UPLO   - CHARACTER*1.
29              On  entry,  UPLO specifies whether the upper or lower triangular
30              part of the array A is to be referenced as follows:
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32              UPLO = 'U' or 'u'   Only the upper triangular part of A is to be
33              referenced.
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35              UPLO = 'L' or 'l'   Only the lower triangular part of A is to be
36              referenced.
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38              Unchanged on exit.
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40       N      - INTEGER.
41              On entry, N specifies the order of the matrix A.  N must  be  at
42              least zero.  Unchanged on exit.
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44       ALPHA  - REAL            .
45              On entry, ALPHA specifies the scalar alpha.  Unchanged on exit.
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47       X      - REAL             array of dimension at least
48              (  1  +  ( n - 1 )*abs( INCX ) ).  Before entry, the incremented
49              array X must contain the n element vector x.  Unchanged on exit.
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51       INCX   - INTEGER.
52              On entry, INCX specifies the increment for the  elements  of  X.
53              INCX must not be zero.  Unchanged on exit.
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55       Y      - REAL             array of dimension at least
56              (  1  +  ( n - 1 )*abs( INCY ) ).  Before entry, the incremented
57              array Y must contain the n element vector y.  Unchanged on exit.
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59       INCY   - INTEGER.
60              On entry, INCY specifies the increment for the  elements  of  Y.
61              INCY must not be zero.  Unchanged on exit.
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63       A      - REAL             array of DIMENSION ( LDA, n ).
64              Before  entry  with  UPLO = 'U' or 'u', the leading n by n upper
65              triangular part of the array A must contain the upper triangular
66              part  of  the symmetric matrix and the strictly lower triangular
67              part of A is not referenced. On exit, the upper triangular  part
68              of  the  array  A is overwritten by the upper triangular part of
69              the updated matrix.  Before entry with UPLO = 'L'  or  'l',  the
70              leading n by n lower triangular part of the array A must contain
71              the lower triangular  part  of  the  symmetric  matrix  and  the
72              strictly  upper triangular part of A is not referenced. On exit,
73              the lower triangular part of the array A is overwritten  by  the
74              lower triangular part of the updated matrix.
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76       LDA    - INTEGER.
77              On  entry, LDA specifies the first dimension of A as declared in
78              the calling (sub) program. LDA must be at least  max(  1,  n  ).
79              Unchanged on exit.
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FURTHER DETAILS

82       Level 2 Blas routine.
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84       -- Written on 22-October-1986.
85          Jack Dongarra, Argonne National Lab.
86          Jeremy Du Croz, Nag Central Office.
87          Sven Hammarling, Nag Central Office.
88          Richard Hanson, Sandia National Labs.
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93BLAS routine                     November 2008                        SSYR2(1)