sgthrz, dgthrz, cgthrz, zgthrz 

Gathers and zeros specified elements of a vector

FORMAT

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

Arguments

  nz                  integer*4
                      On entry, the number of elements to be gathered into
                      the compressed form.
                      On exit, nz 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
                      gathered elements in Y are set to zero. Only the
                      elements in the vector y corresponding to the indices
                      in the INDX array are overwritten.

  x                   real*4 | real*8 | complex*8 | complex*16
                      On entry, an array that receives the specified elements
                      of vector y.
                      On exit, if nz <= 0 x is unchanged. If nz > 0, the
                      array X contains the values gathered into compressed
                      form.

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

Description

  The _GTHRZ subprograms gather the specified elements from a vector y stored
  in full form into a sparse vector x in compressed form. Those elements in y
  are then set to zero.

  For  i=1, ..., nz:

  x(i)  =  y(indx(i)) y(indx (i))  =  0.0

  If nz <= 0, both x and y are unchanged.

  SGTHRZ and DGTHRZ gather the specified elements of a real vector in full
  form into a real sparse vector in compressed form. CGTHRZ and ZGTHRZ gather
  the specified elements of a complex vector in full form into a complex
  sparse vector in compressed form. In each case, the specified elements of
  the full vector are set equal to zero.

Example

  INTEGER NZ, INDX(10)
  REAL*4 Y(40), X(10)
  NZ = 10
  CALL SGTHRZ(NZ, Y, X, INDX)

  This FORTRAN code shows how the nz  elements  of  the  vector y,
  corresponding to the indices in the INDX array, are gathered in a
  compressed form into the vector x.  The gathered  elements in y  are  set
  equal to zero.