SGBT02 computes the residual for a solution of a banded system of


 equations op(A)*X = B:


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


 where op(A) = A or A**T, depending on TRANS, and EPS is the


 machine epsilon.


 The norm used is the 1-norm.

TRANS

          TRANS is CHARACTER*1


          Specifies the form of the system of equations:


          = 'N':  A    * X = B  (No transpose)


          = 'T':  A**T * X = B  (Transpose)


          = 'C':  A**H * X = B  (Conjugate transpose = Transpose)

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.

NRHS

          NRHS is INTEGER


          The number of columns of B.  NRHS >= 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).

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.  If TRANS = 'N',


          LDX >= max(1,N); if TRANS = 'T' or 'C', LDX >= max(1,M).

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.  IF TRANS = 'N',


          LDB >= max(1,M); if TRANS = 'T' or 'C', LDB >= max(1,N).

RWORK

          RWORK is REAL array, dimension (MAX(1,LRWORK)),


          where LRWORK >= M when TRANS = 'T' or 'C'; otherwise, RWORK


          is not referenced.

RESID

          RESID is REAL


          The maximum over the number of right hand sides of


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

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.