# dopgtr.f man page

dopgtr.f —

## Synopsis

### Functions/Subroutines

subroutinedopgtr(UPLO, N, AP, TAU, Q, LDQ, WORK, INFO)DOPGTR

## Function/Subroutine Documentation

### subroutine dopgtr (characterUPLO, integerN, double precision, dimension( * )AP, double precision, dimension( * )TAU, double precision, dimension( ldq, * )Q, integerLDQ, double precision, dimension( * )WORK, integerINFO)

**DOPGTR**

**Purpose:**

```
DOPGTR generates a real orthogonal matrix Q which is defined as the
product of n-1 elementary reflectors H(i) of order n, as returned by
DSPTRD using packed storage:
if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
```

**Parameters:**

*UPLO*

```
UPLO is CHARACTER*1
= 'U': Upper triangular packed storage used in previous
call to DSPTRD;
= 'L': Lower triangular packed storage used in previous
call to DSPTRD.
```

*N*

```
N is INTEGER
The order of the matrix Q. N >= 0.
```

*AP*

```
AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
The vectors which define the elementary reflectors, as
returned by DSPTRD.
```

*TAU*

```
TAU is DOUBLE PRECISION array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary
reflector H(i), as returned by DSPTRD.
```

*Q*

```
Q is DOUBLE PRECISION array, dimension (LDQ,N)
The N-by-N orthogonal matrix Q.
```

*LDQ*

```
LDQ is INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
```

*WORK*

`WORK is DOUBLE PRECISION array, dimension (N-1)`

*INFO*

```
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

Definition at line 115 of file dopgtr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dopgtr(3) is an alias of dopgtr.f(3).