# ?gthr

Gathers a full-storage sparse vector's elements into compressed form.

## Syntax

FORTRAN 77:

call sgthr(nz, y, x, indx )

call dgthr(nz, y, x, indx )

call cgthr(nz, y, x, indx )

call zgthr(nz, y, x, indx )

Fortran 95:

res = gthr(x, indx, y)

## Description

The ?gthr routines gather the specified elements of a full-storage sparse vector y into compressed form(nz, x, indx). The routines reference only the elements of y whose indices are listed in the array indx:

`x(i) = y(indx(i))`, for `i=1,2,... +nz`.

## 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 sgthr

  DOUBLE PRECISION for dgthr

  COMPLEX for cgthr

  DOUBLE COMPLEX for zgthr

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

## Output Parameters

x

  REAL for sgthr

  DOUBLE PRECISION for dgthr

  COMPLEX for cgthr

  DOUBLE COMPLEX for zgthr

  Array, DIMENSION at least nz.

  Contains the vector converted to the compressed form.

## 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 gthr 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