# dgbt01.f - Man Page

TESTING/LIN/dgbt01.f

## Synopsis

### Functions/Subroutines

subroutine dgbt01 (m, n, kl, ku, a, lda, afac, ldafac, ipiv, work, resid)
DGBT01

## Function/Subroutine Documentation

### subroutine dgbt01 (integer m, integer n, integer kl, integer ku, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( ldafac, * ) afac, integer ldafac, integer, dimension( * ) ipiv, double precision, dimension( * ) work, double precision resid)

DGBT01

Purpose:

``` DGBT01 reconstructs a band matrix A from its L*U factorization and
computes the residual:
norm(L*U - A) / ( N * norm(A) * EPS ),
where EPS is the machine epsilon.

The expression L*U - A is computed one column at a time, so A and
AFAC are not modified.```
Parameters

M

```          M is INTEGER
The number of rows of the matrix A.  M >= 0.```

N

```          N is INTEGER
The number of columns of the matrix A.  N >= 0.```

KL

```          KL is INTEGER
The number of subdiagonals within the band of A.  KL >= 0.```

KU

```          KU is INTEGER
The number of superdiagonals within the band of A.  KU >= 0.```

A

```          A is DOUBLE PRECISION array, dimension (LDA,N)
The original matrix A in band storage, stored in rows 1 to
KL+KU+1.```

LDA

```          LDA is INTEGER.
The leading dimension of the array A.  LDA >= max(1,KL+KU+1).```

AFAC

```          AFAC is DOUBLE PRECISION array, dimension (LDAFAC,N)
The factored form of the matrix A.  AFAC contains the banded
factors L and U from the L*U factorization, as computed by
DGBTRF.  U is stored as an upper triangular band matrix with
KL+KU superdiagonals in rows 1 to KL+KU+1, and the
multipliers used during the factorization are stored in rows
KL+KU+2 to 2*KL+KU+1.  See DGBTRF for further details.```

LDAFAC

```          LDAFAC is INTEGER
The leading dimension of the array AFAC.
LDAFAC >= max(1,2*KL*KU+1).```

IPIV

```          IPIV is INTEGER array, dimension (min(M,N))
The pivot indices from DGBTRF.```

WORK

`          WORK is DOUBLE PRECISION array, dimension (2*KL+KU+1)`

RESID

```          RESID is DOUBLE PRECISION
norm(L*U - A) / ( N * norm(A) * EPS )```
Author

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Definition at line 124 of file dgbt01.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dgbt01(3) is an alias of dgbt01.f(3).

Tue Nov 28 2023 12:08:43 Version 3.12.0 LAPACK