Digital

Name

sgthr, dgthr, cgthr, zgthr − Gathers the specified elements of a vector

FORMAT

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

Arguments

nzinteger∗4
On entry, the number of elements to be gathered into the compressed form.
On exit, nz is unchanged. 

yreal∗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. 

xreal∗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. 

indxinteger∗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.