dgbt01.f3

Usage

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

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

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

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

!>          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

Univ. of Colorado Denver

NAG Ltd.

Definition at line 124 of file dgbt01.f.