#include "blaswrap.h"
/*  -- translated by f2c (version 19990503).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Table of constant values */

static integer c__1 = 1;
static doublereal c_b10 = -1.;

/* Subroutine */ int dtbt02_(char *uplo, char *trans, char *diag, integer *n, 
	integer *kd, integer *nrhs, doublereal *ab, integer *ldab, doublereal 
	*x, integer *ldx, doublereal *b, integer *ldb, doublereal *work, 
	doublereal *resid)
{
    /* System generated locals */
    integer ab_dim1, ab_offset, b_dim1, b_offset, x_dim1, x_offset, i__1;
    doublereal d__1, d__2;

    /* Local variables */
    static integer j;
    extern logical lsame_(char *, char *);
    extern doublereal dasum_(integer *, doublereal *, integer *);
    static doublereal anorm, bnorm;
    extern /* Subroutine */ int dcopy_(integer *, doublereal *, integer *, 
	    doublereal *, integer *), dtbmv_(char *, char *, char *, integer *
	    , integer *, doublereal *, integer *, doublereal *, integer *), daxpy_(integer *, doublereal *, 
	    doublereal *, integer *, doublereal *, integer *);
    static doublereal xnorm;
    extern doublereal dlamch_(char *), dlantb_(char *, char *, char *,
	     integer *, integer *, doublereal *, integer *, doublereal *);
    static doublereal eps;


#define b_ref(a_1,a_2) b[(a_2)*b_dim1 + a_1]
#define x_ref(a_1,a_2) x[(a_2)*x_dim1 + a_1]


/*  -- LAPACK test routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       February 29, 1992   


    Purpose   
    =======   

    DTBT02 computes the residual for the computed solution to a   
    triangular system of linear equations  A*x = b  or  A' *x = b when   
    A is a triangular band matrix.  Here A' is the transpose of A and   
    x and b are N by NRHS matrices.  The test ratio is the maximum over   
    the number of right hand sides of   
       norm(b - op(A)*x) / ( norm(op(A)) * norm(x) * EPS ),   
    where op(A) denotes A or A' and EPS is the machine epsilon.   

    Arguments   
    =========   

    UPLO    (input) CHARACTER*1   
            Specifies whether the matrix A is upper or lower triangular.   
            = 'U':  Upper triangular   
            = 'L':  Lower triangular   

    TRANS   (input) CHARACTER*1   
            Specifies the operation applied to A.   
            = 'N':  A *x = b  (No transpose)   
            = 'T':  A'*x = b  (Transpose)   
            = 'C':  A'*x = b  (Conjugate transpose = Transpose)   

    DIAG    (input) CHARACTER*1   
            Specifies whether or not the matrix A is unit triangular.   
            = 'N':  Non-unit triangular   
            = 'U':  Unit triangular   

    N       (input) INTEGER   
            The order of the matrix A.  N >= 0.   

    KD      (input) INTEGER   
            The number of superdiagonals or subdiagonals of the   
            triangular band matrix A.  KD >= 0.   

    NRHS    (input) INTEGER   
            The number of right hand sides, i.e., the number of columns   
            of the matrices X and B.  NRHS >= 0.   

    AB      (input) DOUBLE PRECISION array, dimension (LDAB,N)   
            The upper or lower triangular band matrix A, stored in the   
            first kd+1 rows of the array. The j-th column of A is stored   
            in the j-th column of the array AB as follows:   
            if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;   
            if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).   

    LDAB    (input) INTEGER   
            The leading dimension of the array AB.  LDAB >= KD+1.   

    X       (input) DOUBLE PRECISION array, dimension (LDX,NRHS)   
            The computed solution vectors for the system of linear   
            equations.   

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

    B       (input) DOUBLE PRECISION array, dimension (LDB,NRHS)   
            The right hand side vectors for the system of linear   
            equations.   

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

    WORK    (workspace) DOUBLE PRECISION array, dimension (N)   

    RESID   (output) DOUBLE PRECISION   
            The maximum over the number of right hand sides of   
            norm(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ).   

    =====================================================================   


       Quick exit if N = 0 or NRHS = 0   

       Parameter adjustments */
    ab_dim1 = *ldab;
    ab_offset = 1 + ab_dim1 * 1;
    ab -= ab_offset;
    x_dim1 = *ldx;
    x_offset = 1 + x_dim1 * 1;
    x -= x_offset;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1 * 1;
    b -= b_offset;
    --work;

    /* Function Body */
    if (*n <= 0 || *nrhs <= 0) {
	*resid = 0.;
	return 0;
    }

/*     Compute the 1-norm of A or A'. */

    if (lsame_(trans, "N")) {
	anorm = dlantb_("1", uplo, diag, n, kd, &ab[ab_offset], ldab, &work[1]
		);
    } else {
	anorm = dlantb_("I", uplo, diag, n, kd, &ab[ab_offset], ldab, &work[1]
		);
    }

/*     Exit with RESID = 1/EPS if ANORM = 0. */

    eps = dlamch_("Epsilon");
    if (anorm <= 0.) {
	*resid = 1. / eps;
	return 0;
    }

/*     Compute the maximum over the number of right hand sides of   
          norm(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ). */

    *resid = 0.;
    i__1 = *nrhs;
    for (j = 1; j <= i__1; ++j) {
	dcopy_(n, &x_ref(1, j), &c__1, &work[1], &c__1);
	dtbmv_(uplo, trans, diag, n, kd, &ab[ab_offset], ldab, &work[1], &
		c__1);
	daxpy_(n, &c_b10, &b_ref(1, j), &c__1, &work[1], &c__1);
	bnorm = dasum_(n, &work[1], &c__1);
	xnorm = dasum_(n, &x_ref(1, j), &c__1);
	if (xnorm <= 0.) {
	    *resid = 1. / eps;
	} else {
/* Computing MAX */
	    d__1 = *resid, d__2 = bnorm / anorm / xnorm / eps;
	    *resid = max(d__1,d__2);
	}
/* L10: */
    }

    return 0;

/*     End of DTBT02 */

} /* dtbt02_ */

#undef x_ref
#undef b_ref



.