NAG Library Routine Document

F06EWF (DSCTR)

+− Contents

1 Purpose

9 Example

F06EWF (DSCTR) scatters the elements of a sparse real vector

x

stored in compressed form, into a real vector

y

in full storage form.

SUBROUTINE F06EWF (

INTEGER	NZ, INDX(*)
REAL (KIND=nag_wp)	X(), Y()

The routine may be called by its BLAS name dsctr.

F06EWF (DSCTR) scatters the elements of a vector

x

, stored in compressed form, into a vector,

y

, in full storage form.

Dodson D S, Grimes R G and Lewis J G (1991) Sparse extensions to the Fortran basic linear algebra subprograms ACM Trans. Math. Software 17 253–263

1: NZ – INTEGERInput: On entry: the number of nonzeros in the sparse vector $x$ .
2: X( $*$ ) – REAL (KIND=nag_wp) arrayInput: Note: the dimension of the array X must be at least $\max (1, NZ)$ .
On entry: the nonzero elements of the sparse vector $x$ .
3: INDX( $*$ ) – INTEGER arrayInput: Note: the dimension of the array INDX must be at least $\max (1, NZ)$ .
On entry: $INDX (i)$ must contain the index of $X (i)$ in the sparse vector $x$ , for $i = 1, 2, \dots, NZ$ .
Constraint: the indices must be distinct.
4: Y( $*$ ) – REAL (KIND=nag_wp) arrayOutput: Note: the dimension of the array Y must be at least $\max_{k} \{INDX (k)\}$ .
On exit: the vector $y$ . Only elements corresponding to indices in INDX are altered.