#include "clapack.h"
#include "f2cP.h"

/* Table of constant values */

static integer c__1 = 1;

/* Subroutine */ int dgtcon_(const char *norm, integer *n, double *dl, 
	double *d__, double *du, double *du2, integer *ipiv, 
	double *anorm, double *rcond, double *work, integer *
	iwork, integer *info)
{
    /* System generated locals */
    integer i__1;

    /* Local variables */
    integer i__, kase, kase1;
    integer isave[3];
    double ainvnm;
    bool onenrm;

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

/*     Modified to call DLACN2 in place of DLACON, 5 Feb 03, SJH. */

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

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

/*  DGTCON estimates the reciprocal of the condition number of a real */
/*  tridiagonal matrix A using the LU factorization as computed by */
/*  DGTTRF. */

/*  An estimate is obtained for norm(inv(A)), and the reciprocal of the */
/*  condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))). */

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

/*  NORM    (input) CHARACTER*1 */
/*          Specifies whether the 1-norm condition number or the */
/*          infinity-norm condition number is required: */
/*          = '1' or 'O':  1-norm; */
/*          = 'I':         Infinity-norm. */

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

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

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

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

/*  DU2     (input) DOUBLE PRECISION array, dimension (N-2) */
/*          The (n-2) elements of the second superdiagonal 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. */

/*  ANORM   (input) DOUBLE PRECISION */
/*          If NORM = '1' or 'O', the 1-norm of the original matrix A. */
/*          If NORM = 'I', the infinity-norm of the original matrix A. */

/*  RCOND   (output) DOUBLE PRECISION */
/*          The reciprocal of the condition number of the matrix A, */
/*          computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an */
/*          estimate of the 1-norm of inv(A) computed in this routine. */

/*  WORK    (workspace) DOUBLE PRECISION array, dimension (2*N) */

/*  IWORK   (workspace) INTEGER array, dimension (N) */

/*  INFO    (output) INTEGER */
/*          = 0:  successful exit */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value */

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

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

/*     Test the input arguments. */

    /* Parameter adjustments */
    --iwork;
    --work;
    --ipiv;
    --du2;
    --du;
    --d__;
    --dl;

    /* Function Body */
    *info = 0;
    onenrm = *(unsigned char *)norm == '1' || lsame_(norm, "O");
    if (! onenrm && ! lsame_(norm, "I")) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*anorm < 0.) {
	*info = -8;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DGTCON", &i__1);
	return 0;
    }

/*     Quick return if possible */

    *rcond = 0.;
    if (*n == 0) {
	*rcond = 1.;
	return 0;
    } else if (*anorm == 0.) {
	return 0;
    }

/*     Check that D(1:N) is non-zero. */

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	if (d__[i__] == 0.) {
	    return 0;
	}
/* L10: */
    }

    ainvnm = 0.;
    if (onenrm) {
	kase1 = 1;
    } else {
	kase1 = 2;
    }
    kase = 0;
L20:
    dlacn2_(n, &work[*n + 1], &work[1], &iwork[1], &ainvnm, &kase, isave);
    if (kase != 0) {
	if (kase == kase1) {

/*           Multiply by inv(U)*inv(L). */

	    dgttrs_("No transpose", n, &c__1, &dl[1], &d__[1], &du[1], &du2[1]
, &ipiv[1], &work[1], n, info);
	} else {

/*           Multiply by inv(L')*inv(U'). */

	    dgttrs_("Transpose", n, &c__1, &dl[1], &d__[1], &du[1], &du2[1], &
		    ipiv[1], &work[1], n, info);
	}
	goto L20;
    }

/*     Compute the estimate of the reciprocal condition number. */

    if (ainvnm != 0.) {
	*rcond = 1. / ainvnm / *anorm;
    }

    return 0;

/*     End of DGTCON */

} /* dgtcon_ */
