F06EVF (DGTHRZ) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F06EVF (DGTHRZ)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

+ Contents

    1  Purpose
    7  Accuracy
    9  Example

1  Purpose

F06EVF (DGTHRZ) gathers specified (usually nonzero) elements of a real vector y in full storage form into a sparse real vector x in compressed form. The specified elements of y are set to zero.

2  Specification

SUBROUTINE F06EVF ( NZ, Y, X, INDX)
INTEGER  NZ, INDX(*)
REAL (KIND=nag_wp)  Y(*), X(*)
The routine may be called by its BLAS name dgthrz.

3  Description

F06EVF (DGTHRZ) gathers the specified elements of a vector, y, in full storage form, into the equivalent sparse vector compressed form. The gathered elements of y are set to zero.

4  References

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

5  Parameters

1:     NZ – INTEGERInput
On entry: the number of nonzeros in the compressed sparse vector x.
2:     Y(*) – REAL (KIND=nag_wp) arrayInput/Output
Note: the dimension of the array Y must be at least maxkINDXk .
On entry: the vector y. Only elements corresponding to indices in INDX are accessed.
On exit: the elements of y corresponding to indices in INDX are set to zero.
3:     X(*) – REAL (KIND=nag_wp) arrayOutput
Note: the dimension of the array X must be at least max1,NZ.
On exit: the compressed vector x.
4:     INDX(*) – INTEGER arrayInput
Note: the dimension of the array INDX must be at least max1,NZ .
On entry: INDXi must contain the index Yi, for i=1,2,,NZ, which is to be gathered into x.
Constraint: the indices must be distinct.

6  Error Indicators and Warnings

None.

7  Accuracy

Not applicable.

8  Further Comments

None.

9  Example

None.

F06EVF (DGTHRZ) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012