SGBT01 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.

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 REAL 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 REAL 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
          SGBTRF.  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 SGBTRF 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 SGBTRF.

WORK

          WORK is REAL array, dimension (2*KL+KU+1)

RESID

          RESID is REAL
          norm(L*U - A) / ( N * norm(A) * EPS )

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