# slarzb.f man page

slarzb.f —

## Synopsis

### Functions/Subroutines

subroutineslarzb(SIDE, TRANS, DIRECT, STOREV, M, N, K, L, V, LDV, T, LDT, C, LDC, WORK, LDWORK)SLARZBapplies a block reflector or its transpose to a general matrix.

## Function/Subroutine Documentation

### subroutine slarzb (characterSIDE, characterTRANS, characterDIRECT, characterSTOREV, integerM, integerN, integerK, integerL, real, dimension( ldv, * )V, integerLDV, real, dimension( ldt, * )T, integerLDT, real, dimension( ldc, * )C, integerLDC, real, dimension( ldwork, * )WORK, integerLDWORK)

**SLARZB** applies a block reflector or its transpose to a general matrix.

**Purpose:**

```
SLARZB applies a real block reflector H or its transpose H**T to
a real distributed M-by-N C from the left or the right.
Currently, only STOREV = 'R' and DIRECT = 'B' are supported.
```

**Parameters:**

*SIDE*

```
SIDE is CHARACTER*1
= 'L': apply H or H**T from the Left
= 'R': apply H or H**T from the Right
```

*TRANS*

```
TRANS is CHARACTER*1
= 'N': apply H (No transpose)
= 'C': apply H**T (Transpose)
```

*DIRECT*

```
DIRECT is CHARACTER*1
Indicates how H is formed from a product of elementary
reflectors
= 'F': H = H(1) H(2) . . . H(k) (Forward, not supported yet)
= 'B': H = H(k) . . . H(2) H(1) (Backward)
```

*STOREV*

```
STOREV is CHARACTER*1
Indicates how the vectors which define the elementary
reflectors are stored:
= 'C': Columnwise (not supported yet)
= 'R': Rowwise
```

*M*

```
M is INTEGER
The number of rows of the matrix C.
```

*N*

```
N is INTEGER
The number of columns of the matrix C.
```

*K*

```
K is INTEGER
The order of the matrix T (= the number of elementary
reflectors whose product defines the block reflector).
```

*L*

```
L is INTEGER
The number of columns of the matrix V containing the
meaningful part of the Householder reflectors.
If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0.
```

*V*

```
V is REAL array, dimension (LDV,NV).
If STOREV = 'C', NV = K; if STOREV = 'R', NV = L.
```

*LDV*

```
LDV is INTEGER
The leading dimension of the array V.
If STOREV = 'C', LDV >= L; if STOREV = 'R', LDV >= K.
```

*T*

```
T is REAL array, dimension (LDT,K)
The triangular K-by-K matrix T in the representation of the
block reflector.
```

*LDT*

```
LDT is INTEGER
The leading dimension of the array T. LDT >= K.
```

*C*

```
C is REAL array, dimension (LDC,N)
On entry, the M-by-N matrix C.
On exit, C is overwritten by H*C or H**T*C or C*H or C*H**T.
```

*LDC*

```
LDC is INTEGER
The leading dimension of the array C. LDC >= max(1,M).
```

*WORK*

`WORK is REAL array, dimension (LDWORK,K)`

*LDWORK*

```
LDWORK is INTEGER
The leading dimension of the array WORK.
If SIDE = 'L', LDWORK >= max(1,N);
if SIDE = 'R', LDWORK >= max(1,M).
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

**Contributors:**

A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA

**Further Details:**

Definition at line 183 of file slarzb.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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