#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 doublereal c_b6 = -1.;
static doublereal c_b7 = 1.;
static integer c__1 = 1;

/* Subroutine */ int dgtt02_(char *trans, integer *n, integer *nrhs, 
	doublereal *dl, doublereal *d__, doublereal *du, doublereal *x, 
	integer *ldx, doublereal *b, integer *ldb, doublereal *rwork, 
	doublereal *resid)
{
    /* System generated locals */
    integer 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, xnorm;
    extern doublereal dlamch_(char *);
    extern /* Subroutine */ int dlagtm_(char *, integer *, integer *, 
	    doublereal *, doublereal *, doublereal *, doublereal *, 
	    doublereal *, integer *, doublereal *, doublereal *, integer *);
    extern doublereal dlangt_(char *, integer *, doublereal *, doublereal *, 
	    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   
    =======   

    DGTT02 computes the residual for the solution to a tridiagonal   
    system of equations:   
       RESID = norm(B - op(A)*X) / (norm(A) * norm(X) * EPS),   
    where EPS is the machine epsilon.   

    Arguments   
    =========   

    TRANS   (input) CHARACTER   
            Specifies the form of the residual.   
            = 'N':  B - A * X  (No transpose)   
            = 'T':  B - A'* X  (Transpose)   
            = 'C':  B - A'* X  (Conjugate transpose = Transpose)   

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

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

    DL      (input) DOUBLE PRECISION array, dimension (N-1)   
            The (n-1) sub-diagonal elements of A.   

    D       (input) DOUBLE PRECISION array, dimension (N)   
            The diagonal elements of A.   

    DU      (input) DOUBLE PRECISION array, dimension (N-1)   
            The (n-1) super-diagonal elements of A.   

    X       (input) DOUBLE PRECISION array, dimension (LDX,NRHS)   
            The computed solution vectors X.   

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

    B       (input/output) DOUBLE PRECISION 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 - op(A)*X.   

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

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

    RESID   (output) DOUBLE PRECISION   
            norm(B - op(A)*X) / (norm(A) * norm(X) * EPS)   

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


       Quick exit if N = 0 or NRHS = 0   

       Parameter adjustments */
    --dl;
    --d__;
    --du;
    x_dim1 = *ldx;
    x_offset = 1 + x_dim1 * 1;
    x -= x_offset;
    b_dim1 = *ldb;
    b_offset = 1 + b_dim1 * 1;
    b -= b_offset;
    --rwork;

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

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

    if (lsame_(trans, "N")) {
	anorm = dlangt_("1", n, &dl[1], &d__[1], &du[1]);
    } else {
	anorm = dlangt_("I", n, &dl[1], &d__[1], &du[1]);
    }

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

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

/*     Compute B - op(A)*X. */

    dlagtm_(trans, n, nrhs, &c_b6, &dl[1], &d__[1], &du[1], &x[x_offset], ldx,
	     &c_b7, &b[b_offset], ldb);

    i__1 = *nrhs;
    for (j = 1; j <= i__1; ++j) {
	bnorm = dasum_(n, &b_ref(1, j), &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 DGTT02 */

} /* dgtt02_ */

#undef x_ref
#undef b_ref



.