text: /* dlagts.f -- translated by f2c (version 20061008).
     You must link the resulting object file with libf2c:
  	on Microsoft Windows system, link with libf2c.lib;
  	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
  	or, if you install libf2c.a in a standard place, with -lf2c -lm
  	-- in that order, at the end of the command line, as in
  		cc *.o -lf2c -lm
  	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
  
  		http://www.netlib.org/f2c/libf2c.zip
  */
  
  #include "clapack.h"
  
  
  /* Subroutine */ int dlagts_(integer *job, integer *n, doublereal *a, 
  	doublereal *b, doublereal *c__, doublereal *d__, integer *in, 
  	doublereal *y, doublereal *tol, integer *info)
  {
      /* System generated locals */
      integer i__1;
      doublereal d__1, d__2, d__3, d__4, d__5;
  
      /* Builtin functions */
      double d_sign(doublereal *, doublereal *);
  
      /* Local variables */
      integer k;
      doublereal ak, eps, temp, pert, absak, sfmin;
      extern doublereal dlamch_(char *);
      extern /* Subroutine */ int xerbla_(char *, integer *);
      doublereal bignum;
  
  
  /*  -- LAPACK auxiliary routine (version 3.2) -- */
  /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
  /*     November 2006 */
  
  /*     .. Scalar Arguments .. */
  /*     .. */
  /*     .. Array Arguments .. */
  /*     .. */
  
  /*  Purpose */
  /*  ======= */
  
  /*  DLAGTS may be used to solve one of the systems of equations */
  
  /*     (T - lambda*I)*x = y   or   (T - lambda*I)'*x = y, */
  
  /*  where T is an n by n tridiagonal matrix, for x, following the */
  /*  factorization of (T - lambda*I) as */
  
  /*     (T - lambda*I) = P*L*U , */
  
  /*  by routine DLAGTF. The choice of equation to be solved is */
  /*  controlled by the argument JOB, and in each case there is an option */
  /*  to perturb zero or very small diagonal elements of U, this option */
  /*  being intended for use in applications such as inverse iteration. */
  
  /*  Arguments */
  /*  ========= */
  
  /*  JOB     (input) INTEGER */
  /*          Specifies the job to be performed by DLAGTS as follows: */
  /*          =  1: The equations  (T - lambda*I)x = y  are to be solved, */
  /*                but diagonal elements of U are not to be perturbed. */
  /*          = -1: The equations  (T - lambda*I)x = y  are to be solved */
  /*                and, if overflow would otherwise occur, the diagonal */
  /*                elements of U are to be perturbed. See argument TOL */
  /*                below. */
  /*          =  2: The equations  (T - lambda*I)'x = y  are to be solved, */
  /*                but diagonal elements of U are not to be perturbed. */
  /*          = -2: The equations  (T - lambda*I)'x = y  are to be solved */
  /*                and, if overflow would otherwise occur, the diagonal */
  /*                elements of U are to be perturbed. See argument TOL */
  /*                below. */
  
  /*  N       (input) INTEGER */
  /*          The order of the matrix T. */
  
  /*  A       (input) DOUBLE PRECISION array, dimension (N) */
  /*          On entry, A must contain the diagonal elements of U as */
  /*          returned from DLAGTF. */
  
  /*  B       (input) DOUBLE PRECISION array, dimension (N-1) */
  /*          On entry, B must contain the first super-diagonal elements of */
  /*          U as returned from DLAGTF. */
  
  /*  C       (input) DOUBLE PRECISION array, dimension (N-1) */
  /*          On entry, C must contain the sub-diagonal elements of L as */
  /*          returned from DLAGTF. */
  
  /*  D       (input) DOUBLE PRECISION array, dimension (N-2) */
  /*          On entry, D must contain the second super-diagonal elements */
  /*          of U as returned from DLAGTF. */
  
  /*  IN      (input) INTEGER array, dimension (N) */
  /*          On entry, IN must contain details of the matrix P as returned */
  /*          from DLAGTF. */
  
  /*  Y       (input/output) DOUBLE PRECISION array, dimension (N) */
  /*          On entry, the right hand side vector y. */
  /*          On exit, Y is overwritten by the solution vector x. */
  
  /*  TOL     (input/output) DOUBLE PRECISION */
  /*          On entry, with  JOB .lt. 0, TOL should be the minimum */
  /*          perturbation to be made to very small diagonal elements of U. */
  /*          TOL should normally be chosen as about eps*norm(U), where eps */
  /*          is the relative machine precision, but if TOL is supplied as */
  /*          non-positive, then it is reset to eps*max( abs( u(i,j) ) ). */
  /*          If  JOB .gt. 0  then TOL is not referenced. */
  
  /*          On exit, TOL is changed as described above, only if TOL is */
  /*          non-positive on entry. Otherwise TOL is unchanged. */
  
  /*  INFO    (output) INTEGER */
  /*          = 0   : successful exit */
  /*          .lt. 0: if INFO = -i, the i-th argument had an illegal value */
  /*          .gt. 0: overflow would occur when computing the INFO(th) */
  /*                  element of the solution vector x. This can only occur */
  /*                  when JOB is supplied as positive and either means */
  /*                  that a diagonal element of U is very small, or that */
  /*                  the elements of the right-hand side vector y are very */
  /*                  large. */
  
  /*  ===================================================================== */
  
  /*     .. Parameters .. */
  /*     .. */
  /*     .. Local Scalars .. */
  /*     .. */
  /*     .. Intrinsic Functions .. */
  /*     .. */
  /*     .. External Functions .. */
  /*     .. */
  /*     .. External Subroutines .. */
  /*     .. */
  /*     .. Executable Statements .. */
  
      /* Parameter adjustments */
      --y;
      --in;
      --d__;
      --c__;
      --b;
      --a;
  
      /* Function Body */
      *info = 0;
      if (abs(*job) > 2 || *job == 0) {
  	*info = -1;
      } else if (*n < 0) {
  	*info = -2;
      }
      if (*info != 0) {
  	i__1 = -(*info);
  	xerbla_("DLAGTS", &i__1);
  	return 0;
      }
  
      if (*n == 0) {
  	return 0;
      }
  
      eps = dlamch_("Epsilon");
      sfmin = dlamch_("Safe minimum");
      bignum = 1. / sfmin;
  
      if (*job < 0) {
  	if (*tol <= 0.) {
  	    *tol = abs(a[1]);
  	    if (*n > 1) {
  /* Computing MAX */
  		d__1 = *tol, d__2 = abs(a[2]), d__1 = max(d__1,d__2), d__2 = 
  			abs(b[1]);
  		*tol = max(d__1,d__2);
  	    }
  	    i__1 = *n;
  	    for (k = 3; k <= i__1; ++k) {
  /* Computing MAX */
  		d__4 = *tol, d__5 = (d__1 = a[k], abs(d__1)), d__4 = max(d__4,
  			d__5), d__5 = (d__2 = b[k - 1], abs(d__2)), d__4 = 
  			max(d__4,d__5), d__5 = (d__3 = d__[k - 2], abs(d__3));
  		*tol = max(d__4,d__5);
  /* L10: */
  	    }
  	    *tol *= eps;
  	    if (*tol == 0.) {
  		*tol = eps;
  	    }
  	}
      }
  
      if (abs(*job) == 1) {
  	i__1 = *n;
  	for (k = 2; k <= i__1; ++k) {
  	    if (in[k - 1] == 0) {
  		y[k] -= c__[k - 1] * y[k - 1];
  	    } else {
  		temp = y[k - 1];
  		y[k - 1] = y[k];
  		y[k] = temp - c__[k - 1] * y[k];
  	    }
  /* L20: */
  	}
  	if (*job == 1) {
  	    for (k = *n; k >= 1; --k) {
  		if (k <= *n - 2) {
  		    temp = y[k] - b[k] * y[k + 1] - d__[k] * y[k + 2];
  		} else if (k == *n - 1) {
  		    temp = y[k] - b[k] * y[k + 1];
  		} else {
  		    temp = y[k];
  		}
  		ak = a[k];
  		absak = abs(ak);
  		if (absak < 1.) {
  		    if (absak < sfmin) {
  			if (absak == 0. || abs(temp) * sfmin > absak) {
  			    *info = k;
  			    return 0;
  			} else {
  			    temp *= bignum;
  			    ak *= bignum;
  			}
  		    } else if (abs(temp) > absak * bignum) {
  			*info = k;
  			return 0;
  		    }
  		}
  		y[k] = temp / ak;
  /* L30: */
  	    }
  	} else {
  	    for (k = *n; k >= 1; --k) {
  		if (k <= *n - 2) {
  		    temp = y[k] - b[k] * y[k + 1] - d__[k] * y[k + 2];
  		} else if (k == *n - 1) {
  		    temp = y[k] - b[k] * y[k + 1];
  		} else {
  		    temp = y[k];
  		}
  		ak = a[k];
  		pert = d_sign(tol, &ak);
  L40:
  		absak = abs(ak);
  		if (absak < 1.) {
  		    if (absak < sfmin) {
  			if (absak == 0. || abs(temp) * sfmin > absak) {
  			    ak += pert;
  			    pert *= 2;
  			    goto L40;
  			} else {
  			    temp *= bignum;
  			    ak *= bignum;
  			}
  		    } else if (abs(temp) > absak * bignum) {
  			ak += pert;
  			pert *= 2;
  			goto L40;
  		    }
  		}
  		y[k] = temp / ak;
  /* L50: */
  	    }
  	}
      } else {
  
  /*        Come to here if  JOB = 2 or -2 */
  
  	if (*job == 2) {
  	    i__1 = *n;
  	    for (k = 1; k <= i__1; ++k) {
  		if (k >= 3) {
  		    temp = y[k] - b[k - 1] * y[k - 1] - d__[k - 2] * y[k - 2];
  		} else if (k == 2) {
  		    temp = y[k] - b[k - 1] * y[k - 1];
  		} else {
  		    temp = y[k];
  		}
  		ak = a[k];
  		absak = abs(ak);
  		if (absak < 1.) {
  		    if (absak < sfmin) {
  			if (absak == 0. || abs(temp) * sfmin > absak) {
  			    *info = k;
  			    return 0;
  			} else {
  			    temp *= bignum;
  			    ak *= bignum;
  			}
  		    } else if (abs(temp) > absak * bignum) {
  			*info = k;
  			return 0;
  		    }
  		}
  		y[k] = temp / ak;
  /* L60: */
  	    }
  	} else {
  	    i__1 = *n;
  	    for (k = 1; k <= i__1; ++k) {
  		if (k >= 3) {
  		    temp = y[k] - b[k - 1] * y[k - 1] - d__[k - 2] * y[k - 2];
  		} else if (k == 2) {
  		    temp = y[k] - b[k - 1] * y[k - 1];
  		} else {
  		    temp = y[k];
  		}
  		ak = a[k];
  		pert = d_sign(tol, &ak);
  L70:
  		absak = abs(ak);
  		if (absak < 1.) {
  		    if (absak < sfmin) {
  			if (absak == 0. || abs(temp) * sfmin > absak) {
  			    ak += pert;
  			    pert *= 2;
  			    goto L70;
  			} else {
  			    temp *= bignum;
  			    ak *= bignum;
  			}
  		    } else if (abs(temp) > absak * bignum) {
  			ak += pert;
  			pert *= 2;
  			goto L70;
  		    }
  		}
  		y[k] = temp / ak;
  /* L80: */
  	    }
  	}
  
  	for (k = *n; k >= 2; --k) {
  	    if (in[k - 1] == 0) {
  		y[k - 1] -= c__[k - 1] * y[k];
  	    } else {
  		temp = y[k - 1];
  		y[k - 1] = y[k];
  		y[k] = temp - c__[k - 1] * y[k];
  	    }
  /* L90: */
  	}
      }
  
  /*     End of DLAGTS */
  
      return 0;
  } /* dlagts_ */
  