NAG Library Routine Document

f06erf (ddoti)

1
Purpose

f06erf (ddoti) computes the scalar product of a sparse real vector, stored in compressed form, with a real vector.

2
Specification

Fortran Interface
Function f06erf ( nz, x, indx, y)
Real (Kind=nag_wp):: f06erf
Integer, Intent (In):: nz, indx(*)
Real (Kind=nag_wp), Intent (In):: x(*), y(*)
C Header Interface
#include <nagmk26.h>
double  f06erf_ (const Integer *nz, const double x[], const Integer indx[], const double y[])
The routine may be called by its BLAS name ddoti.

3
Description

f06erf (ddoti) returns, via the function name, the value of the scalar product
xTy = x1 × yindx1 + x2 × yindy2 + + xnz × yindxnz  
where x is a sparse real vector, stored in compressed form and y is a real vector in full storage format.

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
Arguments

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 max1,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 max1,nz .
On entry: indxi must contain the index of xi in the sparse vector x, for i=1,2,,nz.
4:     y* – Real (Kind=nag_wp) arrayInput
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.

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06erf (ddoti) is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.