SPBT01 reconstructs a symmetric positive definite band matrix A from


 its L*L' or U'*U factorization and computes the residual


    norm( L*L' - A ) / ( N * norm(A) * EPS ) or


    norm( U'*U - A ) / ( N * norm(A) * EPS ),


 where EPS is the machine epsilon, L' is the conjugate transpose of


 L, and U' is the conjugate transpose of U.

UPLO

          UPLO is CHARACTER*1


          Specifies whether the upper or lower triangular part of the


          symmetric matrix A is stored:


          = 'U':  Upper triangular


          = 'L':  Lower triangular

N

          N is INTEGER


          The number of rows and columns of the matrix A.  N >= 0.

KD

          KD is INTEGER


          The number of super-diagonals of the matrix A if UPLO = 'U',


          or the number of sub-diagonals if UPLO = 'L'.  KD >= 0.

A

          A is REAL array, dimension (LDA,N)


          The original symmetric band matrix A.  If UPLO = 'U', the


          upper triangular part of A is stored as a band matrix; if


          UPLO = 'L', the lower triangular part of A is stored.  The


          columns of the appropriate triangle are stored in the columns


          of A and the diagonals of the triangle are stored in the rows


          of A.  See SPBTRF for further details.

LDA

          LDA is INTEGER.


          The leading dimension of the array A.  LDA >= max(1,KD+1).

AFAC

          AFAC is REAL array, dimension (LDAFAC,N)


          The factored form of the matrix A.  AFAC contains the factor


          L or U from the L*L' or U'*U factorization in band storage


          format, as computed by SPBTRF.

LDAFAC

          LDAFAC is INTEGER


          The leading dimension of the array AFAC.


          LDAFAC >= max(1,KD+1).

RWORK

          RWORK is REAL array, dimension (N)

RESID

          RESID is REAL


          If UPLO = 'L', norm(L*L' - A) / ( N * norm(A) * EPS )


          If UPLO = 'U', norm(U'*U - A) / ( N * norm(A) * EPS )

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

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