DLA_SYAMV  performs the matrix-vector operation


         y := alpha*abs(A)*abs(x) + beta*abs(y),


 where alpha and beta are scalars, x and y are vectors and A is an


 n by n symmetric matrix.


 This function is primarily used in calculating error bounds.


 To protect against underflow during evaluation, components in


 the resulting vector are perturbed away from zero by (N+1)


 times the underflow threshold.  To prevent unnecessarily large


 errors for block-structure embedded in general matrices,


 "symbolically" zero components are not perturbed.  A zero


 entry is considered "symbolic" if all multiplications involved


 in computing that entry have at least one zero multiplicand.

UPLO

          UPLO is INTEGER


           On entry, UPLO specifies whether the upper or lower


           triangular part of the array A is to be referenced as


           follows:


              UPLO = BLAS_UPPER   Only the upper triangular part of A


                                  is to be referenced.


              UPLO = BLAS_LOWER   Only the lower triangular part of A


                                  is to be referenced.


           Unchanged on exit.

N

          N is INTEGER


           On entry, N specifies the number of columns of the matrix A.


           N must be at least zero.


           Unchanged on exit.

ALPHA

          ALPHA is DOUBLE PRECISION .


           On entry, ALPHA specifies the scalar alpha.


           Unchanged on exit.

A

          A is DOUBLE PRECISION array, dimension ( LDA, n ).


           Before entry, the leading m by n part of the array A must


           contain the matrix of coefficients.


           Unchanged on exit.

LDA

          LDA is INTEGER


           On entry, LDA specifies the first dimension of A as declared


           in the calling (sub) program. LDA must be at least


           max( 1, n ).


           Unchanged on exit.

X

          X is DOUBLE PRECISION array, dimension


           ( 1 + ( n - 1 )*abs( INCX ) )


           Before entry, the incremented array X must contain the


           vector x.


           Unchanged on exit.

INCX

          INCX is INTEGER


           On entry, INCX specifies the increment for the elements of


           X. INCX must not be zero.


           Unchanged on exit.

BETA

          BETA is DOUBLE PRECISION .


           On entry, BETA specifies the scalar beta. When BETA is


           supplied as zero then Y need not be set on input.


           Unchanged on exit.

Y

          Y is DOUBLE PRECISION array, dimension


           ( 1 + ( n - 1 )*abs( INCY ) )


           Before entry with BETA non-zero, the incremented array Y


           must contain the vector y. On exit, Y is overwritten by the


           updated vector y.

INCY

          INCY is INTEGER


           On entry, INCY specifies the increment for the elements of


           Y. INCY must not be zero.


           Unchanged on exit.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

June 2017

  Level 2 Blas routine.


  -- Written on 22-October-1986.


     Jack Dongarra, Argonne National Lab.


     Jeremy Du Croz, Nag Central Office.


     Sven Hammarling, Nag Central Office.


     Richard Hanson, Sandia National Labs.


  -- Modified for the absolute-value product, April 2006


     Jason Riedy, UC Berkeley