f06evf gathers specified (usually nonzero) elements of a real vector in full storage form into a sparse real vector in compressed form. The specified elements of are set to zero.
The routine may be called by the names f06evf, nagf_blas_dgthrz or its BLAS name dgthrz.
3Description
f06evf gathers the specified elements of a vector, , in full storage form, into the equivalent sparse vector compressed form. The gathered elements of are set to zero.
4References
Dodson D S, Grimes R G and Lewis J G (1991) Sparse extensions to the Fortran basic linear algebra subprograms ACM Trans. Math. Software17 253–263
5Arguments
1: – IntegerInput
On entry: the number of nonzeros in the compressed sparse vector .
2: – Real (Kind=nag_wp) arrayInput/Output
Note: the dimension of the array y
must be at least
.
On entry: the vector . Only elements corresponding to indices in indx are accessed.
On exit: the elements of corresponding to indices in indx are set to zero.
3: – Real (Kind=nag_wp) arrayOutput
Note: the dimension of the array x
must be at least
.
On exit: the compressed vector .
4: – Integer arrayInput
Note: the dimension of the array indx
must be at least
.
On entry: must contain the index , for , which is to be gathered into .
Constraint:
the indices must be distinct.
6Error Indicators and Warnings
None.
7Accuracy
Not applicable.
8Parallelism and Performance
Background information to multithreading can be found in the Multithreading documentation.