SPAXPY (3sciport)

Sparse vector plus the product of a scalar and a vector

SYNOPSIS

  Call SPAXPY( n, alpha, x, y, index )

ARGUMENTS

  n               Integer
                  The number of elements in vectors x and y.

  alpha           Real
                  A scalar multiplier.

  x               Real vector.
                  An input vector of length n.

  y               Real vector.
                  A sparse input/output vector of length n.

  index           Integer vector.
                  A vector of indices of vector y.

DESCRIPTION

  A subroutine that is a useful primitive for the lower upper factorization
  and solution of sparse linear systems.  It is defined in FORTRAN in the
  following way:

          DO I=1,N
             Y(INDEX(I)) = Y(INDEX(I)) + ALPHA*X(I)
          ENDDO

  For equations and other information, see Volume 3: UNICOS Math and
  Scientific Library Reference Manual SR-2081 7.0, Cray Research, Inc.