# ?gthrz

Gathers a sparse vector's elements into compressed form, replacing them by zeros.

## Syntax

FORTRAN 77:

call sgthrz(nz, y, x, indx )

call dgthrz(nz, y, x, indx )

call cgthrz(nz, y, x, indx )

call zgthrz(nz, y, x, indx )

Fortran 95:

res = gthrz(x, indx, y)

## Description

The ?gthrz routines gather the elements with indices specified by the array indx from a full-storage vector y into compressed form (nz, x, indx) and overwrite the gathered elements of y by zeros. Other elements of y are not referenced or modified (see also ?gthr).

## Input Parameters

nz

  INTEGER. The number of elements of y to be gathered.

indx

  INTEGER. Specifies indices of elements to be gathered.

  Array, DIMENSION at least nz.

y

  REAL for sgthrz

  DOUBLE PRECISION for dgthrz

  COMPLEX for cgthrz

  DOUBLE COMPLEX for zgthrz

  Array, DIMENSION at least max(indx(i)).

## Output Parameters

x

  REAL for sgthrz

  DOUBLE PRECISION for d gthrz

  COMPLEX for cgthrz

  DOUBLE COMPLEX for zgthrz

  Array, DIMENSION at least nz.

  Contains the vector converted to the compressed form.

y

  The updated vector y.

## Fortran 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see Fortran 95 Interface Conventions.

Specific details for the routine gthrz interface are the following:

x

  Holds the vector of length (nz).

indx

  Holds the vector of length (nz).

y

  Holds the vector of length (nz).

Parent topic: Sparse BLAS Level 1 Routines