#include "f2c.h"
#include "blaswrap.h"

/* Subroutine */ int dgtt01_(integer *n, doublereal *dl, doublereal *d__, 
	doublereal *du, doublereal *dlf, doublereal *df, doublereal *duf, 
	doublereal *du2, integer *ipiv, doublereal *work, integer *ldwork, 
	doublereal *rwork, doublereal *resid)
{
    /* System generated locals */
    integer work_dim1, work_offset, i__1, i__2;

    /* Local variables */
    integer i__, j;
    doublereal li;
    integer ip;
    doublereal eps, anorm;
    integer lastj;
    extern /* Subroutine */ int dswap_(integer *, doublereal *, integer *, 
	    doublereal *, integer *), daxpy_(integer *, doublereal *, 
	    doublereal *, integer *, doublereal *, integer *);
    extern doublereal dlamch_(char *), dlangt_(char *, integer *, 
	    doublereal *, doublereal *, doublereal *), dlanhs_(char *, 
	     integer *, doublereal *, integer *, doublereal *);


/*  -- LAPACK test routine (version 3.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DGTT01 reconstructs a tridiagonal matrix A from its LU factorization */
/*  and computes the residual */
/*     norm(L*U - A) / ( norm(A) * EPS ), */
/*  where EPS is the machine epsilon. */

/*  Arguments */
/*  ========= */

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

/*  DLF     (input) DOUBLE PRECISION array, dimension (N-1) */
/*          The (n-1) multipliers that define the matrix L from the */
/*          LU factorization of A. */

/*  DF      (input) DOUBLE PRECISION array, dimension (N) */
/*          The n diagonal elements of the upper triangular matrix U from */
/*          the LU factorization of A. */

/*  DUF     (input) DOUBLE PRECISION array, dimension (N-1) */
/*          The (n-1) elements of the first super-diagonal of U. */

/*  DU2F    (input) DOUBLE PRECISION array, dimension (N-2) */
/*          The (n-2) elements of the second super-diagonal of U. */

/*  IPIV    (input) INTEGER array, dimension (N) */
/*          The pivot indices; for 1 <= i <= n, row i of the matrix was */
/*          interchanged with row IPIV(i).  IPIV(i) will always be either */
/*          i or i+1; IPIV(i) = i indicates a row interchange was not */
/*          required. */

/*  WORK    (workspace) DOUBLE PRECISION array, dimension (LDWORK,N) */

/*  LDWORK  (input) INTEGER */
/*          The leading dimension of the array WORK.  LDWORK >= max(1,N). */

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

/*  RESID   (output) DOUBLE PRECISION */
/*          The scaled residual:  norm(L*U - A) / (norm(A) * EPS) */

/*  ===================================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Executable Statements .. */

/*     Quick return if possible */

    /* Parameter adjustments */
    --dl;
    --d__;
    --du;
    --dlf;
    --df;
    --duf;
    --du2;
    --ipiv;
    work_dim1 = *ldwork;
    work_offset = 1 + work_dim1;
    work -= work_offset;
    --rwork;

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

    eps = dlamch_("Epsilon");

/*     Copy the matrix U to WORK. */

    i__1 = *n;
    for (j = 1; j <= i__1; ++j) {
	i__2 = *n;
	for (i__ = 1; i__ <= i__2; ++i__) {
	    work[i__ + j * work_dim1] = 0.;
/* L10: */
	}
/* L20: */
    }
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	if (i__ == 1) {
	    work[i__ + i__ * work_dim1] = df[i__];
	    if (*n >= 2) {
		work[i__ + (i__ + 1) * work_dim1] = duf[i__];
	    }
	    if (*n >= 3) {
		work[i__ + (i__ + 2) * work_dim1] = du2[i__];
	    }
	} else if (i__ == *n) {
	    work[i__ + i__ * work_dim1] = df[i__];
	} else {
	    work[i__ + i__ * work_dim1] = df[i__];
	    work[i__ + (i__ + 1) * work_dim1] = duf[i__];
	    if (i__ < *n - 1) {
		work[i__ + (i__ + 2) * work_dim1] = du2[i__];
	    }
	}
/* L30: */
    }

/*     Multiply on the left by L. */

    lastj = *n;
    for (i__ = *n - 1; i__ >= 1; --i__) {
	li = dlf[i__];
	i__1 = lastj - i__ + 1;
	daxpy_(&i__1, &li, &work[i__ + i__ * work_dim1], ldwork, &work[i__ + 
		1 + i__ * work_dim1], ldwork);
	ip = ipiv[i__];
	if (ip == i__) {
/* Computing MIN */
	    i__1 = i__ + 2;
	    lastj = min(i__1,*n);
	} else {
	    i__1 = lastj - i__ + 1;
	    dswap_(&i__1, &work[i__ + i__ * work_dim1], ldwork, &work[i__ + 1 
		    + i__ * work_dim1], ldwork);
	}
/* L40: */
    }

/*     Subtract the matrix A. */

    work[work_dim1 + 1] -= d__[1];
    if (*n > 1) {
	work[(work_dim1 << 1) + 1] -= du[1];
	work[*n + (*n - 1) * work_dim1] -= dl[*n - 1];
	work[*n + *n * work_dim1] -= d__[*n];
	i__1 = *n - 1;
	for (i__ = 2; i__ <= i__1; ++i__) {
	    work[i__ + (i__ - 1) * work_dim1] -= dl[i__ - 1];
	    work[i__ + i__ * work_dim1] -= d__[i__];
	    work[i__ + (i__ + 1) * work_dim1] -= du[i__];
/* L50: */
	}
    }

/*     Compute the 1-norm of the tridiagonal matrix A. */

    anorm = dlangt_("1", n, &dl[1], &d__[1], &du[1]);

/*     Compute the 1-norm of WORK, which is only guaranteed to be */
/*     upper Hessenberg. */

    *resid = dlanhs_("1", n, &work[work_offset], ldwork, &rwork[1])
	    ;

/*     Compute norm(L*U - A) / (norm(A) * EPS) */

    if (anorm <= 0.) {
	if (*resid != 0.) {
	    *resid = 1. / eps;
	}
    } else {
	*resid = *resid / anorm / eps;
    }

    return 0;

/*     End of DGTT01 */

} /* dgtt01_ */