HP MLIB User's Guide Vol. 1 7th Ed.

138 HP MLIB User’s Guide

SSCTR/DSCTR/ISCTR/CSCTR/ZSCTR Scatter sparse vector

indx Array containing the indices {k

} of the interesting

elements of x. The indices must satisfy the following:

where n is the length of y.

Output y Array containing the elements of y, y(i)=y

. If m ≤ 0,

then y is unchanged. Otherwise, only the elements of y

whose indices are included in indx are changed.

Notes The result is unspeciﬁed if any element of indx is out of range, if any two

elements of indx have the same value, or if x, indx, and y overlap such that any

element of x or any index shares a memory location with any element of y.

Fortran

Equivalent

SUBROUTINE SSCTR (M, X,INDX, Y)

REAL*4 X(*),Y(*)

INTEGER*4 INDX(*)

IF ( M .LE. 0 ) RETURN

DO 10 I = 1, M

Y(INDX(I)) = X(I)

10 CONTINUE

RETURN

END

Example Scatter x into y, where x is a sparse vector with interesting elements x

, x

and x

stored in one-dimensional array X, and y is stored in a one-dimensional

array Y of dimension 20.

INTEGER*4 M,INDX(4)

REAL*8 X(4),Y(20)

DATA INDX / 1, 4, 5, 9 /

M = 4

CALL DSCTR (M,X,INDX,Y)

1 indx i() n≤≤i 1=2… m,,,,

indx i() indx j()≠ 1 i≤ j m≤≠,