NAG Library Function Document

nag_dtrttp (f01vac)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

nag_dtrttp (f01vac) copies a real triangular matrix, stored in a full format array, to a standard packed format array.

2
Specification

#include <nag.h>
#include <nagf01.h>
void  nag_dtrttp (Nag_OrderType order, Nag_UploType uplo, Integer n, const double a[], Integer pda, double ap[], NagError *fail)

3
Description

nag_dtrttp (f01vac) packs a real n by n triangular matrix A, stored conventionally in a full format array, into an array of length nn+1/2. The matrix is packed by rows or columns depending on order. This function is intended for possible use in conjunction with functions from Chapters f06, f07, f08 and f16 where some functions use triangular matrices stored in the packed form. Packed storage format is described in Section 3.3.2 in the f07 Chapter Introduction.

4
References

None.

5
Arguments

1:     order Nag_OrderTypeInput
On entry: the order argument specifies the two-dimensional storage scheme being used, i.e., row-major ordering or column-major ordering. C language defined storage is specified by order=Nag_RowMajor. See Section 3.3.1.3 in How to Use the NAG Library and its Documentation for a more detailed explanation of the use of this argument.
Constraint: order=Nag_RowMajor or Nag_ColMajor.
2:     uplo Nag_UploTypeInput
On entry: specifies whether A is upper or lower triangular.
uplo=Nag_Upper
A is upper triangular.
uplo=Nag_Lower
A is lower triangular.
Constraint: uplo=Nag_Upper or Nag_Lower.
3:     n IntegerInput
On entry: n, the order of the matrix A.
Constraint: n0.
4:     a[dim] const doubleInput
Note: the dimension, dim, of the array a must be at least pda×n.
On entry: the triangular matrix A.
If order=Nag_ColMajor, Aij is stored in a[j-1×pda+i-1].
If order=Nag_RowMajor, Aij is stored in a[i-1×pda+j-1].
If uplo=Nag_Upper, the upper triangular part of A must be stored and the elements of the array below the diagonal are not referenced.
If uplo=Nag_Lower, the lower triangular part of A must be stored and the elements of the array above the diagonal are not referenced.
5:     pda IntegerInput
On entry: the stride separating row or column elements (depending on the value of order) of the matrix A in the array a.
Constraint: pdamax1,n.
6:     ap[dim] doubleOutput
Note: the dimension, dim, of the array ap must be at least n×n+1/2.
On exit: the n by n triangular matrix A, packed by rows or columns depending on order.
The storage of elements Aij depends on the order and uplo arguments as follows:
  • if order=Nag_ColMajor and uplo=Nag_Upper,
              Aij is stored in ap[j-1×j/2+i-1], for ij;
  • if order=Nag_ColMajor and uplo=Nag_Lower,
              Aij is stored in ap[2n-j×j-1/2+i-1], for ij;
  • if order=Nag_RowMajor and uplo=Nag_Upper,
              Aij is stored in ap[2n-i×i-1/2+j-1], for ij;
  • if order=Nag_RowMajor and uplo=Nag_Lower,
              Aij is stored in ap[i-1×i/2+j-1], for ij.
7:     fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INT
On entry, n=value.
Constraint: n0.
NE_INT_2
On entry, pda=value and n=value.
Constraint: pdamax1,n.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7
Accuracy

Not applicable.

8
Parallelism and Performance

nag_dtrttp (f01vac) is not threaded in any implementation.

9
Further Comments

None.

10
Example

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

10.1
Program Text

Program Text (f01vace.c)

10.2
Program Data

Program Data (f01vace.d)

10.3
Program Results

Program Results (f01vace.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017