NAG Library Routine Document

F08FTF (ZUNGTR)

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     $\mathrm{UPLO}$ – CHARACTER(1)Input

On entry: this must be the same parameter UPLO as supplied to F08FSF (ZHETRD).

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

2:     $\mathrm{N}$ – INTEGERInput

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

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

3:     $\mathrm{A}\left(\mathbf{LDA},*\right)$ – COMPLEX (KIND=nag_wp) arrayInput/Output

Note: the second dimension of the array A must be at least $\max \left(1,\mathbf{N}\right)$.

On entry: details of the vectors which define the elementary reflectors, as returned by F08FSF (ZHETRD).

On exit: the $n$ by $n$ unitary matrix $Q$.

4:     $\mathrm{LDA}$ – INTEGERInput

On entry: the first dimension of the array A as declared in the (sub)program from which F08FTF (ZUNGTR) is called.

Constraint: $\mathbf{LDA}\ge \max \left(1,\mathbf{N}\right)$.

5:     $\mathrm{TAU}\left(*\right)$ – COMPLEX (KIND=nag_wp) arrayInput

Note: the dimension of the array TAU must be at least $\max \left(1,\mathbf{N}-1\right)$.

On entry: further details of the elementary reflectors, as returned by F08FSF (ZHETRD).

6:     $\mathrm{WORK}\left(\max \left(1,\mathbf{LWORK}\right)\right)$ – COMPLEX (KIND=nag_wp) arrayWorkspace

On exit: if $\mathbf{INFO}=\mathbf{0}$, the real part of $\mathbf{WORK}\left(1\right)$ contains the minimum value of LWORK required for optimal performance.

7:     $\mathrm{LWORK}$ – INTEGERInput

On entry: the dimension of the array WORK as declared in the (sub)program from which F08FTF (ZUNGTR) is called.

If $\mathbf{LWORK}=-1$, a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this value as the first entry of the WORK array, and no error message related to LWORK is issued.

Suggested value: for optimal performance, $\mathbf{LWORK}\ge \left(\mathbf{N}-1\right)\times \mathit{nb}$, where $\mathit{nb}$ is the optimal block size.

Constraint: $\mathbf{LWORK}\ge \max \left(1,\mathbf{N}-1\right)$ or $\mathbf{LWORK}=-1$.

8:     $\mathrm{INFO}$ – INTEGEROutput

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

6  Error Indicators and Warnings

$\mathbf{INFO}<0$

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

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example

10.1  Program Text

Program Text (f08ftfe.f90)

10.2  Program Data

Program Data (f08ftfe.d)

10.3  Program Results

Program Results (f08ftfe.r)