SPDOT (3sciport)

Dot product of a vector and a sparse vector

SYNOPSIS

  result = SPDOT( n, x, index, y )

FUNCTION VALUE

  spdot           Real
                  The inner product of vector x and sparse vector y.

ARGUMENTS

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

  x               Real vector.
                  An input vector of length n.

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

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

DESCRIPTION

  A real function 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
             SPDOT = SPDOT + X(I)*Y(INDEX(I))
          ENDDO

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