sgthr, dgthr, cgthr, zgthr 

Gathers the specified elements of a vector

FORMAT

  {S,D,C,Z}GTHR ( 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, y is unchanged.  Only the elements in the
                      vector y corresponding to the indices in the INDX array
                      are accessed.

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

Description

  The _GTHR subprograms gather specified elements from a vector in full form,
  y, and store them as a vector x in compressed form.

  For i = 1, ..., nz:

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

  If nz <= 0, x is unchanged.

  SGTHR and DGTHR gather the specified elements from a real vector in full
  form and store them as a real sparse vector in compressed form.  CGTHR and
  ZGTHR gather the specified elements from a complex vector in full form and
  store them as a complex sparse vector in compressed form.

Example

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