DDOTI(3)                MathKeisan SPARSE BLAS routine                DDOTI(3)



NAME
       DDOTI - Double precision indexed dot product

SYNOPSIS
       DOUBLE PRECISION FUNCTION DDOTI( NZ, X, INDX, Y )

           INTEGER        NZ, INDX

           DOUBLE PRECISION
                          X, Y

PURPOSE
       Sdoti  computes  the  vector inner product of a double precision sparse
       vector X stored in compressed form ( X, INDX ) with a double  precision
       vector Y in full storage form. Only the elements of Y whose indices are
       listed in INDX are referenced.
       DDOTI computes:
                               NZ
          DOTI  <--  X * Y  =  Sum  X(i) * Y( INDX(i) )
                               i=1
       where X and Y are double precision vectors.

ARGUMENTS
       DDOTI   (output) DOUBLE PRECISION
               Double function value equal to the vector inner product.

       NZ      (input) INTEGER
               Number of elements in the compressed form.

       X       (input) DOUBLE PRECISION
               Array containing the values of the compressed form.

       INDX    (input) INTEGER
               Array containing the indices of  the  compressed  form.  It  is
               assumed that the elements in INDX are distinct.

       Y       (input) DOUBLE PRECISION
               Array,  on  input,  which contains the vector Y in full storage
               form. Only the elements corresponding to the  indices  in  INDX
               will be accessed.

FURTHER DETAILS
       Sparse  BLAS  algorithm  is  from  ACM  algorithm  692 by D. Dodson, R.
       Grimes, and J. Lewis.


SEE ALSO
       sblas(3)



MathKeisan                         June 1991                          DDOTI(3)