NAG FL Interface
f01vef (dtrttf)

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1 Purpose

f01vef copies a real triangular matrix, stored in a full format array, to a Rectangular Full Packed (RFP) format array.

2 Specification

Fortran Interface
Subroutine f01vef ( transr, uplo, n, a, lda, ar, info)
Integer, Intent (In) :: n, lda
Integer, Intent (Out) :: info
Real (Kind=nag_wp), Intent (In) :: a(lda,*)
Real (Kind=nag_wp), Intent (Out) :: ar(n*(n+1)/2)
Character (1), Intent (In) :: transr, uplo
C Header Interface
#include <nag.h>
void  f01vef_ (const char *transr, const char *uplo, const Integer *n, const double a[], const Integer *lda, double ar[], Integer *info, const Charlen length_transr, const Charlen length_uplo)
The routine may be called by the names f01vef, nagf_matop_dtrttf or its LAPACK name dtrttf.

3 Description

f01vef packs a real n×n triangular matrix A, stored conventionally in a full format array, into RFP format. This routine is intended for possible use in conjunction with routines from Chapters F06, F07 and F16 where some routines that use triangular matrices store them in RFP format. The RFP storage format is described in Section 3.3.3 in the F07 Chapter Introduction.

4 References

Gustavson F G, Waśniewski J, Dongarra J J and Langou J (2010) Rectangular full packed format for Cholesky's algorithm: factorization, solution, and inversion ACM Trans. Math. Software 37, 2

5 Arguments

1: transr Character(1) Input
On entry: specifies whether the normal RFP representation of A or its transpose is stored.
transr='N'
The RFP representation of the matrix A is stored.
transr='T'
The transpose of the RFP representation of the matrix A is stored.
Constraint: transr='N' or 'T'.
2: uplo Character(1) Input
On entry: specifies whether A is upper or lower triangular.
uplo='U'
A is upper triangular.
uplo='L'
A is lower triangular.
Constraint: uplo='U' or 'L'.
3: n Integer Input
On entry: n, the order of the matrix A.
Constraint: n0.
4: a(lda,*) Real (Kind=nag_wp) array Input
Note: the second dimension of the array a must be at least n.
On entry: the triangular matrix A.
  • If uplo='U', A is upper triangular and the elements of the array below the diagonal are not referenced.
  • If uplo='L', A is lower triangular and the elements of the array above the diagonal are not referenced.
5: lda Integer Input
On entry: the first dimension of the array a as declared in the (sub)program from which f01vef is called.
Constraint: ldamax(1,n).
6: ar(n×(n+1)/2) Real (Kind=nag_wp) array Output
On exit: the upper or lower n×n triangular matrix A (as specified by uplo) in either normal or transposed RFP format (as specified by transr). The storage format is described in Section 3.3.3 in the F07 Chapter Introduction.
7: info Integer Output
On exit: info=0 unless the routine detects an error (see Section 6).

6 Error Indicators and Warnings

info<0
If info=-i, argument i had an illegal value. An explanatory message is output, and execution of the program is terminated.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
f01vef is not threaded in any implementation.

9 Further Comments

None.

10 Example

This example reads in a triangular matrix and copies it to RFP format.

10.1 Program Text

Program Text (f01vefe.f90)

10.2 Program Data

Program Data (f01vefe.d)

10.3 Program Results

Program Results (f01vefe.r)