slong
hypgeom_estimate_terms(const mag_t z, int r, slong prec)
{
double y, t;
t = mag_get_d(z);
if (t == 0)
return 1;
if (r == 0)
{
if (t >= 1)
{
flint_printf("z must be smaller than 1\n");
abort();
}
y = (log(1-t) - prec * LOG2) / log(t) + 1;
}
else
{
y = (prec * LOG2) / (d_root(t, r) * EXP1 * r);
y = (prec * LOG2) / (r * d_lambertw(y)) + 1;
}
if (y >= WORD_MAX / 2)
{
flint_printf("error: series will converge too slowly\n");
abort();
}
return y;
}
slong
_arb_mat_exp_choose_N(const mag_t norm, slong prec)
{
if (mag_is_special(norm) || mag_cmp_2exp_si(norm, 30) > 0 ||
mag_cmp_2exp_si(norm, -prec) < 0)
{
return 1;
}
else if (mag_cmp_2exp_si(norm, -300) < 0)
{
slong N = -MAG_EXP(norm);
return (prec + N - 1) / N;
}
else
{
double c, t;
c = mag_get_d(norm);
t = d_lambertw(prec * LOG2_OVER_E / c);
t = c * exp(t + 1.0);
return FLINT_MIN((slong) (t + 1.0), 2 * prec);
}
}
void
acb_hypgeom_airy(acb_t ai, acb_t aip, acb_t bi, acb_t bip, const acb_t z, slong prec)
{
arf_srcptr re, im;
double x, y, t, zmag, z15, term_est, airy_est, abstol;
slong n, wp;
if (!acb_is_finite(z))
{
if (ai != NULL) acb_indeterminate(ai);
if (aip != NULL) acb_indeterminate(aip);
if (bi != NULL) acb_indeterminate(bi);
if (bip != NULL) acb_indeterminate(bip);
return;
}
re = arb_midref(acb_realref(z));
im = arb_midref(acb_imagref(z));
wp = prec * 1.03 + 15;
/* tiny input -- use direct method and pick n without underflowing */
if (arf_cmpabs_2exp_si(re, -64) < 0 && arf_cmpabs_2exp_si(im, -64) < 0)
{
if (arf_cmpabs_2exp_si(re, -wp) < 0 && arf_cmpabs_2exp_si(im, -wp) < 0)
{
n = 1; /* very tiny input */
}
else
{
if (arf_cmpabs(re, im) > 0)
zmag = fmpz_get_d(ARF_EXPREF(re));
else
zmag = fmpz_get_d(ARF_EXPREF(im));
zmag = (zmag + 1) * (1.0 / LOG2);
n = wp / (-zmag) + 1;
}
acb_hypgeom_airy_direct(ai, aip, bi, bip, z, n, wp);
} /* huge input -- use asymptotics and pick n without overflowing */
else if ((arf_cmpabs_2exp_si(re, 64) > 0 || arf_cmpabs_2exp_si(im, 64) > 0))
{
if (arf_cmpabs_2exp_si(re, prec) > 0 || arf_cmpabs_2exp_si(im, prec) > 0)
{
n = 1; /* very huge input */
}
else
{
x = fmpz_get_d(ARF_EXPREF(re));
y = fmpz_get_d(ARF_EXPREF(im));
zmag = (FLINT_MAX(x, y) - 2) * (1.0 / LOG2);
n = asymp_pick_terms(wp, zmag);
n = FLINT_MAX(n, 1);
}
acb_hypgeom_airy_asymp(ai, aip, bi, bip, z, n, wp);
}
else /* moderate input */
{
x = arf_get_d(re, ARF_RND_DOWN);
y = arf_get_d(im, ARF_RND_DOWN);
zmag = sqrt(x * x + y * y);
z15 = zmag * sqrt(zmag);
if (zmag >= 4.0 && (n = asymp_pick_terms(wp, log(zmag))) != -1)
{
acb_hypgeom_airy_asymp(ai, aip, bi, bip, z, n, wp);
}
else if (zmag <= 1.5)
{
t = 3 * (wp * LOG2) / (2 * z15 * EXP1);
t = (wp * LOG2) / (2 * d_lambertw(t));
n = FLINT_MAX(t + 1, 2);
acb_hypgeom_airy_direct(ai, aip, bi, bip, z, n, wp);
}
else
{
/* estimate largest term: log2(exp(2(z^3/9)^(1/2))) */
term_est = 0.96179669392597560491 * z15;
/* estimate the smaller of Ai and Bi */
airy_est = estimate_airy(x, y, (ai != NULL || aip != NULL));
/* estimate absolute tolerance and necessary working precision */
abstol = airy_est - wp;
wp = wp + term_est - airy_est;
wp = FLINT_MAX(wp, 10);
t = 3 * (-abstol * LOG2) / (2 * z15 * EXP1);
t = (-abstol * LOG2) / (2 * d_lambertw(t));
n = FLINT_MAX(t + 1, 2);
if (acb_is_exact(z))
acb_hypgeom_airy_direct(ai, aip, bi, bip, z, n, wp);
else
acb_hypgeom_airy_direct_prop(ai, aip, bi, bip, z, n, wp);
}
}
if (ai != NULL) acb_set_round(ai, ai, prec);
if (aip != NULL) acb_set_round(aip, aip, prec);
if (bi != NULL) acb_set_round(bi, bi, prec);
if (bip != NULL) acb_set_round(bip, bip, prec);
}
