NAG Library Routine Document

f01vlf  (dtfttp)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:     $\mathbf{transr}$ – Character(1)Input

On entry: specifies whether the normal RFP representation of $A$ or its transpose is stored.

$\mathbf{transr}=\text{'N'}$

The RFP representation of the matrix $A$ is stored.

$\mathbf{transr}=\text{'T'}$

The transpose of the RFP representation of the matrix $A$ is stored.

Constraint: $\mathbf{transr}=\text{'N'}$ or $\text{'T'}$.

2:     $\mathbf{uplo}$ – Character(1)Input

On entry: specifies whether $A$ is upper or lower triangular.

$\mathbf{uplo}=\text{'U'}$

$A$ is upper triangular.

$\mathbf{uplo}=\text{'L'}$

$A$ is lower triangular.

Constraint: $\mathbf{uplo}=\text{'U'}$ or $\text{'L'}$.

3:     $\mathbf{n}$ – IntegerInput

On entry: $n$, the order of the matrix $A$.

Constraint: $\mathbf{n}\ge 0$.

4:     $\mathbf{ar}\left(\mathbf{n}\times \left(\mathbf{n}+1\right)/2\right)$ – Real (Kind=nag_wp) arrayInput

On entry: the upper or lower $n$ by $n$ 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.

5:     $\mathbf{ap}\left(\mathbf{n}\times \left(\mathbf{n}+1\right)/2\right)$ – Real (Kind=nag_wp) arrayOutput

On exit: the $n$ by $n$ triangular matrix $A$, packed by columns.

More precisely,

• if $\mathbf{uplo}=\text{'U'}$, the upper triangle of $A$ is stored with element $A_{ij}$ in $\mathbf{ap}\left(i+j\left(j-1\right)/2\right)$ for $i\le j$;
• if $\mathbf{uplo}=\text{'L'}$, the lower triangle of $A$ is stored with element $A_{ij}$ in $\mathbf{ap}\left(i+\left(2n-j\right)\left(j-1\right)/2\right)$ for $i\ge j$.

6:     $\mathbf{info}$ – IntegerOutput

On exit: $\mathbf{info}=0$ unless the routine detects an error (see Section 6).

6

Error Indicators and Warnings

$-999<\mathbf{info}<0$

If $\mathbf{info}=-i$, argument $i$ had an illegal value. An explanatory message is output, and execution of the program is terminated.

$\mathbf{info}=-999$

Dynamic memory allocation failed.

See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

Program Text (f01vlfe.f90)

10.2

Program Data

Program Data (f01vlfe.d)

10.3

Program Results

Program Results (f01vlfe.r)