SAXPYI(3)    SPARSE BLAS routine of NEC Numeric Library Collection   SAXPYI(3)



NAME
       SAXPYI - indexed real elementary vector operation

SYNOPSIS
       SUBROUTINE SAXPYI( NZ, A, X, INDX, Y )

           INTEGER        NZ, INDX

           REAL           A, X

PURPOSE
       SAXPYI  adds a real scalar multiple of a real sparse vector X stored in
       compressed form ( X, INDX ) to a real vector Y in  full  storage  form.
       Only the elements of Y whose indices are listed in  INDX are referenced
       or modified.

       This routine performs the following vector operation:

                 Y  <--  A*X + Y

       which is the FORTRAN 77 operation

            Y(INDX(I)) = A*X(I) + Y(INDX(I))  for I = 1, ..., NZ

       The value in INDX must be distinct to allow consistent vector or paral-
       lel execution.

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

       A       (input) REAL
               Scalar multiplier of X.

       X       (input) REAL
               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, output) REAL
               Array, on input, which contains the vector Y  in  full  storage
               form.  On output only the elements corresponding to the indices
               in INDX have been modified.


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




SPARSE BLAS routine             31 October 2017                      SAXPYI(3)