/* Copyright (c) 1992-2008 The University of Tennessee.  All rights reserved.
 * See file COPYING in this directory for details. */

#ifdef __cplusplus
extern "C" {
#endif

#include "f2c.h"
#include "hypre_lapack.h"

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

/* Subroutine */ integer dlasq4_(integer *i0, integer *n0, doublereal *z__,
	integer *pp, integer *n0in, doublereal *dmin__, doublereal *dmin1,
	doublereal *dmin2, doublereal *dn, doublereal *dn1, doublereal *dn2,
	doublereal *tau, integer *ttype)
{
    /* Initialized data */
    doublereal g = 0.;

    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2;

    /* Local variables */
    doublereal s, a2, b1, b2;
    integer i4, nn, np;
    doublereal gam, gap1, gap2;


/*  -- LAPACK auxiliary routine (version 3.0) --
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
       Courant Institute, Argonne National Lab, and Rice University
       October 31, 1999


    Purpose
    =======

    DLASQ4 computes an approximation TAU to the smallest eigenvalue
    using values of d from the previous transform.

    I0    (input) INTEGER
          First index.

    N0    (input) INTEGER
          Last index.

    Z     (input) DOUBLE PRECISION array, dimension ( 4*N )
          Z holds the qd array.

    PP    (input) INTEGER
          PP=0 for ping, PP=1 for pong.

    NOIN  (input) INTEGER
          The value of N0 at start of EIGTEST.

    DMIN  (input) DOUBLE PRECISION
          Minimum value of d.

    DMIN1 (input) DOUBLE PRECISION
          Minimum value of d, excluding D( N0 ).

    DMIN2 (input) DOUBLE PRECISION
          Minimum value of d, excluding D( N0 ) and D( N0-1 ).

    DN    (input) DOUBLE PRECISION
          d(N)

    DN1   (input) DOUBLE PRECISION
          d(N-1)

    DN2   (input) DOUBLE PRECISION
          d(N-2)

    TAU   (output) DOUBLE PRECISION
          This is the shift.

    TTYPE (output) INTEGER
          Shift type.

    Further Details
    ===============
    CNST1 = 9/16

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

       Parameter adjustments */
    --z__;
    s = 0.;

    /* Function Body

       A negative DMIN forces the shift to take that absolute value
       TTYPE records the type of shift. */

    if (*dmin__ <= 0.) {
	*tau = -(*dmin__);
	*ttype = -1;
	return 0;
    }

    nn = (*n0 << 2) + *pp;
    if (*n0in == *n0) {

/*        No eigenvalues deflated. */

	if (*dmin__ == *dn || *dmin__ == *dn1) {

	    b1 = sqrt(z__[nn - 3]) * sqrt(z__[nn - 5]);
	    b2 = sqrt(z__[nn - 7]) * sqrt(z__[nn - 9]);
	    a2 = z__[nn - 7] + z__[nn - 5];

/*           Cases 2 and 3. */

	    if (*dmin__ == *dn && *dmin1 == *dn1) {
		gap2 = *dmin2 - a2 - *dmin2 * .25;
		if (gap2 > 0. && gap2 > b2) {
		    gap1 = a2 - *dn - b2 / gap2 * b2;
		} else {
		    gap1 = a2 - *dn - (b1 + b2);
		}
		if (gap1 > 0. && gap1 > b1) {
/* Computing MAX */
		    d__1 = *dn - b1 / gap1 * b1, d__2 = *dmin__ * .5;
		    s = max(d__1,d__2);
		    *ttype = -2;
		} else {
		    s = 0.;
		    if (*dn > b1) {
			s = *dn - b1;
		    }
		    if (a2 > b1 + b2) {
/* Computing MIN */
			d__1 = s, d__2 = a2 - (b1 + b2);
			s = min(d__1,d__2);
		    }
/* Computing MAX */
		    d__1 = s, d__2 = *dmin__ * .333;
		    s = max(d__1,d__2);
		    *ttype = -3;
		}
	    } else {

/*              Case 4. */

		*ttype = -4;
		s = *dmin__ * .25;
		if (*dmin__ == *dn) {
		    gam = *dn;
		    a2 = 0.;
		    if (z__[nn - 5] > z__[nn - 7]) {
			return 0;
		    }
		    b2 = z__[nn - 5] / z__[nn - 7];
		    np = nn - 9;
		} else {
		    np = nn - (*pp << 1);
		    b2 = z__[np - 2];
		    gam = *dn1;
		    if (z__[np - 4] > z__[np - 2]) {
			return 0;
		    }
		    a2 = z__[np - 4] / z__[np - 2];
		    if (z__[nn - 9] > z__[nn - 11]) {
			return 0;
		    }
		    b2 = z__[nn - 9] / z__[nn - 11];
		    np = nn - 13;
		}

/*              Approximate contribution to norm squared from I < NN-1. */

		a2 += b2;
		i__1 = (*i0 << 2) - 1 + *pp;
		for (i4 = np; i4 >= i__1; i4 += -4) {
		    if (b2 == 0.) {
			goto L20;
		    }
		    b1 = b2;
		    if (z__[i4] > z__[i4 - 2]) {
			return 0;
		    }
		    b2 *= z__[i4] / z__[i4 - 2];
		    a2 += b2;
		    if (max(b2,b1) * 100. < a2 || .563 < a2) {
			goto L20;
		    }
/* L10: */
		}
L20:
		a2 *= 1.05;

/*              Rayleigh quotient residual bound. */

		if (a2 < .563) {
		    s = gam * (1. - sqrt(a2)) / (a2 + 1.);
		}
	    }
	} else if (*dmin__ == *dn2) {

/*           Case 5. */

	    *ttype = -5;
	    s = *dmin__ * .25;

/*           Compute contribution to norm squared from I > NN-2. */

	    np = nn - (*pp << 1);
	    b1 = z__[np - 2];
	    b2 = z__[np - 6];
	    gam = *dn2;
	    if (z__[np - 8] > b2 || z__[np - 4] > b1) {
		return 0;
	    }
	    a2 = z__[np - 8] / b2 * (z__[np - 4] / b1 + 1.);

/*           Approximate contribution to norm squared from I < NN-2. */

	    if (*n0 - *i0 > 2) {
		b2 = z__[nn - 13] / z__[nn - 15];
		a2 += b2;
		i__1 = (*i0 << 2) - 1 + *pp;
		for (i4 = nn - 17; i4 >= i__1; i4 += -4) {
		    if (b2 == 0.) {
			goto L40;
		    }
		    b1 = b2;
		    if (z__[i4] > z__[i4 - 2]) {
			return 0;
		    }
		    b2 *= z__[i4] / z__[i4 - 2];
		    a2 += b2;
		    if (max(b2,b1) * 100. < a2 || .563 < a2) {
			goto L40;
		    }
/* L30: */
		}
L40:
		a2 *= 1.05;
	    }

	    if (a2 < .563) {
		s = gam * (1. - sqrt(a2)) / (a2 + 1.);
	    }
	} else {

/*           Case 6, no information to guide us. */

	    if (*ttype == -6) {
		g += (1. - g) * .333;
	    } else if (*ttype == -18) {
		g = .083250000000000005;
	    } else {
		g = .25;
	    }
	    s = g * *dmin__;
	    *ttype = -6;
	}

    } else if (*n0in == *n0 + 1) {

/*        One eigenvalue just deflated. Use DMIN1, DN1 for DMIN and DN. */

	if (*dmin1 == *dn1 && *dmin2 == *dn2) {

/*           Cases 7 and 8. */

	    *ttype = -7;
	    s = *dmin1 * .333;
	    if (z__[nn - 5] > z__[nn - 7]) {
		return 0;
	    }
	    b1 = z__[nn - 5] / z__[nn - 7];
	    b2 = b1;
	    if (b2 == 0.) {
		goto L60;
	    }
	    i__1 = (*i0 << 2) - 1 + *pp;
	    for (i4 = (*n0 << 2) - 9 + *pp; i4 >= i__1; i4 += -4) {
		a2 = b1;
		if (z__[i4] > z__[i4 - 2]) {
		    return 0;
		}
		b1 *= z__[i4] / z__[i4 - 2];
		b2 += b1;
		if (max(b1,a2) * 100. < b2) {
		    goto L60;
		}
/* L50: */
	    }
L60:
	    b2 = sqrt(b2 * 1.05);
/* Computing 2nd power */
	    d__1 = b2;
	    a2 = *dmin1 / (d__1 * d__1 + 1.);
	    gap2 = *dmin2 * .5 - a2;
	    if (gap2 > 0. && gap2 > b2 * a2) {
/* Computing MAX */
		d__1 = s, d__2 = a2 * (1. - a2 * 1.01 * (b2 / gap2) * b2);
		s = max(d__1,d__2);
	    } else {
/* Computing MAX */
		d__1 = s, d__2 = a2 * (1. - b2 * 1.01);
		s = max(d__1,d__2);
		*ttype = -8;
	    }
	} else {

/*           Case 9. */

	    s = *dmin1 * .25;
	    if (*dmin1 == *dn1) {
		s = *dmin1 * .5;
	    }
	    *ttype = -9;
	}

    } else if (*n0in == *n0 + 2) {

/*        Two eigenvalues deflated. Use DMIN2, DN2 for DMIN and DN.

          Cases 10 and 11. */

	if (*dmin2 == *dn2 && z__[nn - 5] * 2. < z__[nn - 7]) {
	    *ttype = -10;
	    s = *dmin2 * .333;
	    if (z__[nn - 5] > z__[nn - 7]) {
		return 0;
	    }
	    b1 = z__[nn - 5] / z__[nn - 7];
	    b2 = b1;
	    if (b2 == 0.) {
		goto L80;
	    }
	    i__1 = (*i0 << 2) - 1 + *pp;
	    for (i4 = (*n0 << 2) - 9 + *pp; i4 >= i__1; i4 += -4) {
		if (z__[i4] > z__[i4 - 2]) {
		    return 0;
		}
		b1 *= z__[i4] / z__[i4 - 2];
		b2 += b1;
		if (b1 * 100. < b2) {
		    goto L80;
		}
/* L70: */
	    }
L80:
	    b2 = sqrt(b2 * 1.05);
/* Computing 2nd power */
	    d__1 = b2;
	    a2 = *dmin2 / (d__1 * d__1 + 1.);
	    gap2 = z__[nn - 7] + z__[nn - 9] - sqrt(z__[nn - 11]) * sqrt(z__[
		    nn - 9]) - a2;
	    if (gap2 > 0. && gap2 > b2 * a2) {
/* Computing MAX */
		d__1 = s, d__2 = a2 * (1. - a2 * 1.01 * (b2 / gap2) * b2);
		s = max(d__1,d__2);
	    } else {
/* Computing MAX */
		d__1 = s, d__2 = a2 * (1. - b2 * 1.01);
		s = max(d__1,d__2);
	    }
	} else {
	    s = *dmin2 * .25;
	    *ttype = -11;
	}
    } else if (*n0in > *n0 + 2) {

/*        Case 12, more than two eigenvalues deflated. No information. */

	s = 0.;
	*ttype = -12;
    }

    *tau = s;
    return 0;

/*     End of DLASQ4 */

} /* dlasq4_ */

#ifdef __cplusplus
}
#endif
