ssumi, dsumi, csumi, zsumi 

Sum of a vector and a sparse vector

FORMAT

  {S,D,C,Z}SUMI ( nz, x, indx, y )

Arguments

  nz                  integer*4
                      On entry, the number of elements in the vector in the
                      compressed form.
                      On exit, nz is unchanged.

  x                   real*4 | real*8 | complex*8 | complex*16
                      On entry, an array of the elements of vector x in
                      compressed form.
                      On exit, x is unchanged.

  indx                integer*4
                      On entry, an array containing the indices of the
                      compressed form. The values in the INDX array must be
                      distinct for consistent vector or parallel execution.
                      On exit, indx is unchanged.

  y                   real*4 | real*8 | complex*8 | complex*16
                      On entry, an array of the elements of vector y stored
                      in full form.
                      On exit, if nz <= 0, y is unchanged. If nz > 0, the
                      elements in the vector y corresponding to the indices
                      in the INDX array are overwritten.

Description

  SSUMI and DSUMI add a sparse vector of real values stored in compressed
  form to a real vector stored in full form. CSUMI and ZSUMI add a sparse
  vector of complex values stored in compressed form to a complex vector
  stored in full form.

  Only the elements of vector y whose indices are listed in array INDX are
  overwritten.

  For i =1, ..., nz:

  y(indx(i)) =  y(indx(i)) +  x(i)

  If nz <= 0, y is unchanged.

  The _SUMI subprograms are an efficient implementation of the _AXPYI
  subprograms when alpha = 1.0.

  The _SUMI subprograms are not part of the original set of Sparse BLAS Level
  1 subprograms.

Example

  INTEGER NZ, INDX(20)
  REAL*8 Y(100), X(20)
  NZ = 20
  CALL DSUMI(NZ, X, INDX, Y)

  This FORTRAN code shows how the nz elements in y, corresponding to the
  indices  in  the array INDX, are  updated by  the  addition  of the
  corresponding element of the compressed vector, x.