#include "clapack.h" /* Subroutine */ int dlazq4_(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, doublereal *g) { /* System generated locals */ integer i__1; doublereal d__1, d__2; /* Builtin functions */ double sqrt(doublereal); /* Local variables */ doublereal s, a2, b1, b2; integer i4, nn, np; doublereal gam, gap1, gap2; /* -- LAPACK auxiliary routine (version 3.1) -- */ /* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */ /* November 2006 */ /* .. Scalar Arguments .. */ /* .. */ /* .. Array Arguments .. */ /* .. */ /* Purpose */ /* ======= */ /* DLAZQ4 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. */ /* N0IN (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. */ /* G (input/output) DOUBLE PRECISION */ /* G is passed as an argument in order to save its value between */ /* calls to DLAZQ4 */ /* Further Details */ /* =============== */ /* CNST1 = 9/16 */ /* This is a thread safe version of DLASQ4, which passes G through the */ /* argument list in place of declaring G in a SAVE statment. */ /* ===================================================================== */ /* .. Parameters .. */ /* .. */ /* .. Local Scalars .. */ /* .. */ /* .. Intrinsic Functions .. */ /* .. */ /* .. Executable Statements .. */ /* A negative DMIN forces the shift to take that absolute value */ /* TTYPE records the type of shift. */ /* Parameter adjustments */ --z__; /* Function Body */ 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 DLAZQ4 */ } /* dlazq4_ */