SPBT02 computes the residual for a solution of a symmetric banded


 system of equations  A*x = b:


    RESID = norm( B - A*X ) / ( norm(A) * norm(X) * EPS)


 where EPS is the machine precision.

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.

NRHS

          NRHS is INTEGER


          The number of right hand sides. NRHS >= 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).

X

          X is REAL array, dimension (LDX,NRHS)


          The computed solution vectors for the system of linear


          equations.

LDX

          LDX is INTEGER


          The leading dimension of the array X.   LDX >= max(1,N).

B

          B is REAL array, dimension (LDB,NRHS)


          On entry, the right hand side vectors for the system of


          linear equations.


          On exit, B is overwritten with the difference B - A*X.

LDB

          LDB is INTEGER


          The leading dimension of the array B.  LDB >= max(1,N).

RWORK

          RWORK is REAL array, dimension (N)

RESID

          RESID is REAL


          The maximum over the number of right hand sides of


          norm(B - A*X) / ( norm(A) * norm(X) * EPS ).

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