/* this can be improved */
static int
use_recurrence(const acb_t n, const acb_t a, const acb_t b, slong prec)
{
if (!acb_is_int(n) || !arb_is_nonnegative(acb_realref(n)))
return 0;
if (arf_cmpabs_ui(arb_midref(acb_realref(n)), prec) > 0)
return 0;
if (arb_is_nonnegative(acb_realref(a)) ||
arf_get_d(arb_midref(acb_realref(a)), ARF_RND_DOWN) > -0.9)
return 0;
return 1;
}
void
acb_rising(acb_t y, const acb_t x, const acb_t n, long prec)
{
if (acb_is_int(n) && arf_sgn(arb_midref(acb_realref(n))) >= 0 &&
arf_cmpabs_ui(arb_midref(acb_realref(n)), FLINT_MAX(prec, 100)) < 0)
{
acb_rising_ui_rec(y, x,
arf_get_si(arb_midref(acb_realref(n)), ARF_RND_DOWN), prec);
}
else
{
acb_t t;
acb_init(t);
acb_add(t, x, n, prec);
acb_gamma(t, t, prec);
acb_rgamma(y, x, prec);
acb_mul(y, y, t, prec);
acb_clear(t);
}
}
void
_arb_poly_rgamma_series(arb_ptr res, arb_srcptr h, long hlen, long len, long prec)
{
int reflect;
long i, rflen, r, n, wp;
arb_ptr t, u, v;
arb_struct f[2];
hlen = FLINT_MIN(hlen, len);
wp = prec + FLINT_BIT_COUNT(prec);
t = _arb_vec_init(len);
u = _arb_vec_init(len);
v = _arb_vec_init(len);
arb_init(f);
arb_init(f + 1);
/* use zeta values at small integers */
if (arb_is_int(h) && (arf_cmpabs_ui(arb_midref(h), prec / 2) < 0))
{
r = arf_get_si(arb_midref(h), ARF_RND_DOWN);
_arb_poly_lgamma_series_at_one(u, len, wp);
_arb_vec_neg(u, u, len);
_arb_poly_exp_series(t, u, len, len, wp);
if (r == 1)
{
_arb_vec_swap(v, t, len);
}
else if (r <= 0)
{
arb_set(f, h);
arb_one(f + 1);
rflen = FLINT_MIN(len, 2 - r);
_arb_poly_rising_ui_series(u, f, FLINT_MIN(2, len), 1 - r, rflen, wp);
_arb_poly_mullow(v, t, len, u, rflen, len, wp);
}
else
{
arb_one(f);
arb_one(f + 1);
rflen = FLINT_MIN(len, r);
_arb_poly_rising_ui_series(v, f, FLINT_MIN(2, len), r - 1, rflen, wp);
/* TODO: use div_series? */
_arb_poly_inv_series(u, v, rflen, len, wp);
_arb_poly_mullow(v, t, len, u, len, len, wp);
}
}
else
{
/* otherwise use Stirling series */
arb_gamma_stirling_choose_param(&reflect, &r, &n, h, 1, 0, wp);
/* rgamma(h) = (gamma(1-h+r) sin(pi h)) / (rf(1-h, r) * pi), h = h0 + t*/
if (reflect)
{
/* u = gamma(r+1-h) */
arb_sub_ui(f, h, r + 1, wp);
arb_neg(f, f);
_arb_poly_gamma_stirling_eval(t, f, n, len, wp);
_arb_poly_exp_series(u, t, len, len, wp);
for (i = 1; i < len; i += 2)
arb_neg(u + i, u + i);
/* v = sin(pi x) */
arb_const_pi(f + 1, wp);
arb_mul(f, h, f + 1, wp);
_arb_poly_sin_series(v, f, 2, len, wp);
_arb_poly_mullow(t, u, len, v, len, len, wp);
/* rf(1-h,r) * pi */
if (r == 0)
{
arb_const_pi(u, wp);
_arb_vec_scalar_div(v, t, len, u, wp);
}
else
{
arb_sub_ui(f, h, 1, wp);
arb_neg(f, f);
arb_set_si(f + 1, -1);
rflen = FLINT_MIN(len, r + 1);
_arb_poly_rising_ui_series(v, f, FLINT_MIN(2, len), r, rflen, wp);
arb_const_pi(u, wp);
_arb_vec_scalar_mul(v, v, rflen, u, wp);
/* divide by rising factorial */
/* TODO: might better to use div_series, when it has a good basecase */
_arb_poly_inv_series(u, v, rflen, len, wp);
_arb_poly_mullow(v, t, len, u, len, len, wp);
}
}
else
{
/* rgamma(h) = rgamma(h+r) rf(h,r) */
if (r == 0)
{
arb_add_ui(f, h, r, wp);
_arb_poly_gamma_stirling_eval(t, f, n, len, wp);
_arb_vec_neg(t, t, len);
_arb_poly_exp_series(v, t, len, len, wp);
}
else
{
arb_set(f, h);
arb_one(f + 1);
rflen = FLINT_MIN(len, r + 1);
_arb_poly_rising_ui_series(t, f, FLINT_MIN(2, len), r, rflen, wp);
arb_add_ui(f, h, r, wp);
_arb_poly_gamma_stirling_eval(v, f, n, len, wp);
_arb_vec_neg(v, v, len);
_arb_poly_exp_series(u, v, len, len, wp);
_arb_poly_mullow(v, u, len, t, rflen, len, wp);
}
}
}
/* compose with nonconstant part */
arb_zero(t);
_arb_vec_set(t + 1, h + 1, hlen - 1);
_arb_poly_compose_series(res, v, len, t, hlen, len, prec);
arb_clear(f);
arb_clear(f + 1);
_arb_vec_clear(t, len);
_arb_vec_clear(u, len);
_arb_vec_clear(v, len);
}
/* derivatives: |8/sqrt(pi) sin(2z^2)|, |8/sqrt(pi) cos(2z^2)| <= 5 exp(4|xy|) */
void
acb_hypgeom_fresnel_erf_error(acb_t res1, acb_t res2, const acb_t z, slong prec)
{
mag_t re;
mag_t im;
acb_t zmid;
mag_init(re);
mag_init(im);
acb_init(zmid);
if (arf_cmpabs_ui(arb_midref(acb_realref(z)), 1000) < 0 &&
arf_cmpabs_ui(arb_midref(acb_imagref(z)), 1000) < 0)
{
arb_get_mag(re, acb_realref(z));
arb_get_mag(im, acb_imagref(z));
mag_mul(re, re, im);
mag_mul_2exp_si(re, re, 2);
mag_exp(re, re);
mag_mul_ui(re, re, 5);
}
else
{
arb_t t;
arb_init(t);
arb_mul(t, acb_realref(z), acb_imagref(z), prec);
arb_abs(t, t);
arb_mul_2exp_si(t, t, 2);
arb_exp(t, t, prec);
arb_get_mag(re, t);
mag_mul_ui(re, re, 5);
arb_clear(t);
}
mag_hypot(im, arb_radref(acb_realref(z)), arb_radref(acb_imagref(z)));
mag_mul(re, re, im);
if (arb_is_zero(acb_imagref(z)))
{
mag_set_ui(im, 8); /* For real x, |S(x)| < 4, |C(x)| < 4. */
mag_min(re, re, im);
mag_zero(im);
}
else if (arb_is_zero(acb_realref(z)))
{
mag_set_ui(im, 8);
mag_min(im, re, im);
mag_zero(re);
}
else
{
mag_set(im, re);
}
arf_set(arb_midref(acb_realref(zmid)), arb_midref(acb_realref(z)));
arf_set(arb_midref(acb_imagref(zmid)), arb_midref(acb_imagref(z)));
acb_hypgeom_fresnel_erf(res1, res2, zmid, prec);
if (res1 != NULL)
{
arb_add_error_mag(acb_realref(res1), re);
arb_add_error_mag(acb_imagref(res1), im);
}
if (res2 != NULL)
{
arb_add_error_mag(acb_realref(res2), re);
arb_add_error_mag(acb_imagref(res2), im);
}
mag_clear(re);
mag_clear(im);
acb_clear(zmid);
}
void
acb_hypgeom_erf_asymp(acb_t res, const acb_t z, int complementary, slong prec, slong prec2)
{
acb_t a, t, u;
acb_init(a);
acb_init(t);
acb_init(u);
if (!acb_is_exact(z) &&
(arf_cmpabs_ui(arb_midref(acb_realref(z)), prec) < 0) &&
(arf_cmpabs_ui(arb_midref(acb_imagref(z)), prec) < 0))
{
acb_t zmid;
mag_t re_err, im_err;
acb_init(zmid);
mag_init(re_err);
mag_init(im_err);
acb_hypgeom_erf_propagated_error(re_err, im_err, z);
arf_set(arb_midref(acb_realref(zmid)), arb_midref(acb_realref(z)));
arf_set(arb_midref(acb_imagref(zmid)), arb_midref(acb_imagref(z)));
acb_hypgeom_erf_asymp(res, zmid, complementary, prec, prec2);
arb_add_error_mag(acb_realref(res), re_err);
arb_add_error_mag(acb_imagref(res), im_err);
acb_clear(zmid);
mag_clear(re_err);
mag_clear(im_err);
return;
}
acb_one(a);
acb_mul_2exp_si(a, a, -1);
acb_mul(t, z, z, prec2);
acb_hypgeom_u_asymp(u, a, a, t, -1, prec2);
acb_neg(t, t);
acb_exp(t, t, prec2);
acb_mul(u, u, t, prec2);
arb_const_sqrt_pi(acb_realref(t), prec2);
arb_zero(acb_imagref(t));
acb_mul(t, t, z, prec2);
acb_div(u, u, t, prec2);
/* branch cut term: -1 or 1 */
acb_csgn(acb_realref(t), z);
arb_zero(acb_imagref(t));
if (complementary)
{
/* erfc(z) = 1 - erf(z) = u - (sgn - 1) */
acb_sub_ui(t, t, 1, prec);
acb_sub(t, u, t, prec);
}
else
{
/* erf(z) = sgn - u */
acb_sub(t, t, u, prec);
}
if (arb_is_zero(acb_imagref(z)))
{
arb_zero(acb_imagref(t));
}
else if (arb_is_zero(acb_realref(z)))
{
if (complementary)
arb_one(acb_realref(t));
else
arb_zero(acb_realref(t));
}
acb_set(res, t);
acb_clear(a);
acb_clear(t);
acb_clear(u);
}
void
acb_hypgeom_2f1(acb_t res, const acb_t a, const acb_t b,
const acb_t c, const acb_t z, int flags, slong prec)
{
int algorithm, regularized;
regularized = flags & ACB_HYPGEOM_2F1_REGULARIZED;
if (!acb_is_finite(a) || !acb_is_finite(b) || !acb_is_finite(c) || !acb_is_finite(z))
{
acb_indeterminate(res);
return;
}
if (acb_is_zero(z))
{
if (regularized)
acb_rgamma(res, c, prec);
else
acb_one(res);
return;
}
if (regularized && acb_is_int(c) && arb_is_nonpositive(acb_realref(c)))
{
if ((acb_is_int(a) && arb_is_nonpositive(acb_realref(a)) &&
arf_cmp(arb_midref(acb_realref(a)), arb_midref(acb_realref(c))) >= 0) ||
(acb_is_int(b) && arb_is_nonpositive(acb_realref(b)) &&
arf_cmp(arb_midref(acb_realref(b)), arb_midref(acb_realref(c))) >= 0))
{
acb_zero(res);
return;
}
}
if (regularized && acb_eq(a, c))
{
_acb_hypgeom_2f1r_reduced(res, b, c, z, prec);
return;
}
if (regularized && acb_eq(b, c))
{
_acb_hypgeom_2f1r_reduced(res, a, c, z, prec);
return;
}
/* polynomial */
if (acb_is_int(a) && arf_sgn(arb_midref(acb_realref(a))) <= 0 &&
arf_cmpabs_ui(arb_midref(acb_realref(a)), prec) < 0)
{
acb_hypgeom_2f1_direct(res, a, b, c, z, regularized, prec);
return;
}
/* polynomial */
if (acb_is_int(b) && arf_sgn(arb_midref(acb_realref(b))) <= 0 &&
arf_cmpabs_ui(arb_midref(acb_realref(b)), prec) < 0)
{
acb_hypgeom_2f1_direct(res, a, b, c, z, regularized, prec);
return;
}
/* Try to reduce to a polynomial case using the Pfaff transformation */
/* TODO: look at flags for integer c-b, c-a here, even when c is nonexact */
if (acb_is_exact(c))
{
acb_t t;
acb_init(t);
acb_sub(t, c, b, prec);
if (acb_is_int(t) && arb_is_nonpositive(acb_realref(t)))
{
acb_hypgeom_2f1_transform(res, a, b, c, z, flags, 1, prec);
acb_clear(t);
return;
}
acb_sub(t, c, a, prec);
if (acb_is_int(t) && arb_is_nonpositive(acb_realref(t)))
{
int f1, f2;
/* When swapping a, b, also swap the flags. */
f1 = flags & ACB_HYPGEOM_2F1_AC;
f2 = flags & ACB_HYPGEOM_2F1_BC;
flags &= ~ACB_HYPGEOM_2F1_AC;
flags &= ~ACB_HYPGEOM_2F1_BC;
if (f1) flags |= ACB_HYPGEOM_2F1_BC;
if (f2) flags |= ACB_HYPGEOM_2F1_AC;
acb_hypgeom_2f1_transform(res, b, a, c, z, flags, 1, prec);
acb_clear(t);
return;
}
acb_clear(t);
}
/* special value at z = 1 */
if (acb_is_one(z))
{
acb_t t, u, v;
acb_init(t);
acb_init(u);
acb_init(v);
acb_sub(t, c, a, prec);
acb_sub(u, c, b, prec);
acb_sub(v, t, b, prec);
if (arb_is_positive(acb_realref(v)))
{
acb_rgamma(t, t, prec);
acb_rgamma(u, u, prec);
acb_mul(t, t, u, prec);
acb_gamma(v, v, prec);
acb_mul(t, t, v, prec);
if (!regularized)
{
acb_gamma(v, c, prec);
acb_mul(t, t, v, prec);
}
acb_set(res, t);
}
else
{
acb_indeterminate(res);
}
acb_clear(t);
acb_clear(u);
acb_clear(v);
return;
}
algorithm = acb_hypgeom_2f1_choose(z);
if (algorithm == 0)
{
acb_hypgeom_2f1_direct(res, a, b, c, z, regularized, prec);
}
else if (algorithm >= 1 && algorithm <= 5)
{
acb_hypgeom_2f1_transform(res, a, b, c, z, flags, algorithm, prec);
}
else
{
acb_hypgeom_2f1_corner(res, a, b, c, z, regularized, prec);
}
}
void
_arb_poly_lgamma_series(arb_ptr res, arb_srcptr h, slong hlen, slong len, slong prec)
{
int reflect;
slong r, n, wp;
arb_t zr;
arb_ptr t, u;
if (!arb_is_positive(h))
{
_arb_vec_indeterminate(res, len);
return;
}
hlen = FLINT_MIN(hlen, len);
wp = prec + FLINT_BIT_COUNT(prec);
t = _arb_vec_init(len);
u = _arb_vec_init(len);
arb_init(zr);
/* use zeta values at small integers */
if (arb_is_int(h) && (arf_cmpabs_ui(arb_midref(h), prec / 2) < 0))
{
r = arf_get_si(arb_midref(h), ARF_RND_DOWN);
if (r <= 0)
{
_arb_vec_indeterminate(res, len);
goto cleanup;
}
else
{
_arb_poly_lgamma_series_at_one(u, len, wp);
if (r != 1)
{
arb_one(zr);
_log_rising_ui_series(t, zr, r - 1, len, wp);
_arb_vec_add(u, u, t, len, wp);
}
}
}
else if (len <= 2)
{
arb_lgamma(u, h, wp);
if (len == 2)
arb_digamma(u + 1, h, wp);
}
else
{
/* otherwise use Stirling series */
arb_gamma_stirling_choose_param(&reflect, &r, &n, h, 0, 0, wp);
arb_add_ui(zr, h, r, wp);
_arb_poly_gamma_stirling_eval(u, zr, n, len, wp);
if (r != 0)
{
_log_rising_ui_series(t, h, r, len, wp);
_arb_vec_sub(u, u, t, len, wp);
}
}
/* compose with nonconstant part */
arb_zero(t);
_arb_vec_set(t + 1, h + 1, hlen - 1);
_arb_poly_compose_series(res, u, len, t, hlen, len, prec);
cleanup:
arb_clear(zr);
_arb_vec_clear(t, len);
_arb_vec_clear(u, len);
}
void acb_hypgeom_u_asymp(acb_t res, const acb_t a, const acb_t b,
const acb_t z, slong n, slong prec)
{
acb_struct aa[3];
acb_t s, t, w, winv;
int R, p, q, is_real, is_terminating;
slong n_terminating;
if (!acb_is_finite(a) || !acb_is_finite(b) || !acb_is_finite(z))
{
acb_indeterminate(res);
return;
}
acb_init(aa);
acb_init(aa + 1);
acb_init(aa + 2);
acb_init(s);
acb_init(t);
acb_init(w);
acb_init(winv);
is_terminating = 0;
n_terminating = WORD_MAX;
/* special case, for incomplete gamma
[todo: also when they happen to be exact and with difference 1...] */
if (a == b)
{
acb_set(aa, a);
p = 1;
q = 0;
}
else
{
acb_set(aa, a);
acb_sub(aa + 1, a, b, prec);
acb_add_ui(aa + 1, aa + 1, 1, prec);
acb_one(aa + 2);
p = 2;
q = 1;
}
if (acb_is_nonpositive_int(aa))
{
is_terminating = 1;
if (arf_cmpabs_ui(arb_midref(acb_realref(aa)), prec) < 0)
n_terminating = 1 - arf_get_si(arb_midref(acb_realref(aa)), ARF_RND_DOWN);
}
if (p == 2 && acb_is_nonpositive_int(aa + 1))
{
is_terminating = 1;
if (arf_cmpabs_ui(arb_midref(acb_realref(aa + 1)), n_terminating) < 0)
n_terminating = 1 - arf_get_si(arb_midref(acb_realref(aa + 1)), ARF_RND_DOWN);
}
acb_neg(w, z);
acb_inv(w, w, prec);
acb_neg(winv, z);
/* low degree polynomial -- no need to try to terminate sooner */
if (is_terminating && n_terminating < 8)
{
acb_hypgeom_pfq_sum_invz(s, t, aa, p, aa + p, q, w, winv,
n_terminating, prec);
acb_set(res, s);
}
else
{
mag_t C1, Cn, alpha, nu, sigma, rho, zinv, tmp, err;
mag_init(C1);
mag_init(Cn);
mag_init(alpha);
mag_init(nu);
mag_init(sigma);
mag_init(rho);
mag_init(zinv);
mag_init(tmp);
mag_init(err);
acb_hypgeom_u_asymp_bound_factors(&R, alpha, nu,
sigma, rho, zinv, a, b, z);
is_real = acb_is_real(a) && acb_is_real(b) && acb_is_real(z) &&
(is_terminating || arb_is_positive(acb_realref(z)));
if (R == 0)
{
/* if R == 0, the error bound is infinite unless terminating */
if (is_terminating && n_terminating < prec)
{
acb_hypgeom_pfq_sum_invz(s, t, aa, p, aa + p, q, w, winv,
n_terminating, prec);
acb_set(res, s);
}
else
{
acb_indeterminate(res);
}
}
else
{
/* C1 */
acb_hypgeom_mag_Cn(C1, R, nu, sigma, 1);
/* err = 2 * alpha * exp(...) */
mag_mul(tmp, C1, rho);
mag_mul(tmp, tmp, alpha);
mag_mul(tmp, tmp, zinv);
mag_mul_2exp_si(tmp, tmp, 1);
mag_exp(err, tmp);
mag_mul(err, err, alpha);
mag_mul_2exp_si(err, err, 1);
/* choose n automatically */
if (n < 0)
{
slong moreprec;
/* take err into account when finding truncation point */
/* we should take Cn into account as well, but this depends
on n which is to be determined; it's easier to look
only at exp(...) which should be larger anyway */
if (mag_cmp_2exp_si(err, 10 * prec) > 0)
moreprec = 10 * prec;
else if (mag_cmp_2exp_si(err, 0) < 0)
moreprec = 0;
else
moreprec = MAG_EXP(err);
n = acb_hypgeom_pfq_choose_n_max(aa, p, aa + p, q, w,
prec + moreprec, FLINT_MIN(WORD_MAX / 2, 50 + 10.0 * prec));
}
acb_hypgeom_pfq_sum_invz(s, t, aa, p, aa + p, q, w, winv, n, prec);
/* add error bound, if not terminating */
if (!(is_terminating && n == n_terminating))
{
acb_hypgeom_mag_Cn(Cn, R, nu, sigma, n);
mag_mul(err, err, Cn);
/* nth term * factor */
acb_get_mag(tmp, t);
mag_mul(err, err, tmp);
if (is_real)
arb_add_error_mag(acb_realref(s), err);
else
acb_add_error_mag(s, err);
}
acb_set(res, s);
}
mag_clear(C1);
mag_clear(Cn);
mag_clear(alpha);
mag_clear(nu);
mag_clear(sigma);
mag_clear(rho);
mag_clear(zinv);
mag_clear(tmp);
mag_clear(err);
}
acb_clear(aa);
acb_clear(aa + 1);
acb_clear(aa + 2);
acb_clear(s);
acb_clear(t);
acb_clear(w);
acb_clear(winv);
}
void
acb_hypgeom_pfq_series_direct(acb_poly_t res,
const acb_poly_struct * a, long p,
const acb_poly_struct * b, long q,
const acb_poly_t z, int regularized,
long n, long len, long prec)
{
acb_poly_t s, t, err;
arb_poly_t C, T;
long i;
int is_real;
int terminating;
/* default algorithm to choose number of terms */
if (n < 0)
{
n = acb_hypgeom_pfq_series_choose_n(a, p, b, q, z, len, prec);
}
terminating = 0;
/* check if it terminates due to a root of the numerator */
for (i = 0; i < p; i++)
{
if (acb_poly_length(a + i) == 0 && n > 0)
{
terminating = 1;
}
else if (acb_poly_length(a + i) == 1)
{
acb_srcptr c = acb_poly_get_coeff_ptr(a + i, 0);
if (acb_is_int(c) && arb_is_negative(acb_realref(c)) &&
arf_cmpabs_ui(arb_midref(acb_realref(c)), n) < 0)
{
terminating = 1;
}
}
}
/* check if it terminates (to order n) due to z */
/* the following tests could be made stronger... */
if (z->length == 0 && n >= 1)
{
terminating = 1;
}
else if (!terminating && z->length > 0 && acb_is_zero(z->coeffs) && n >= len)
{
if (regularized)
{
terminating = 1;
}
else
{
terminating = 1;
for (i = 0; i < q; i++)
{
acb_srcptr c = acb_poly_get_coeff_ptr(b + i, 0);
if (!arb_is_positive(acb_realref(c)) && acb_contains_int(c))
terminating = 0;
}
}
}
acb_poly_init(s);
acb_poly_init(t);
acb_poly_init(err);
arb_poly_init(C);
arb_poly_init(T);
acb_hypgeom_pfq_series_sum_forward(s, t, a, p, b, q, z, regularized, n, len, prec);
if (!terminating)
{
is_real = acb_poly_is_real(z);
for (i = 0; i < p; i++)
is_real = is_real && acb_poly_is_real(a + i);
for (i = 0; i < q; i++)
is_real = is_real && acb_poly_is_real(b + i);
acb_poly_majorant(T, t, MAG_BITS);
acb_hypgeom_pfq_series_bound_factor(C, a, p, b, q, z, n, len, MAG_BITS);
if (!_arb_vec_is_finite(T->coeffs, T->length) ||
!_arb_vec_is_finite(C->coeffs, C->length))
{
arb_poly_fit_length(T, len);
_arb_vec_indeterminate(T->coeffs, len);
_arb_poly_set_length(T, len);
}
else
{
arb_poly_mullow(T, T, C, len, MAG_BITS);
}
/* create polynomial of errors */
acb_poly_fit_length(err, len);
for (i = 0; i < FLINT_MIN(len, T->length); i++)
{
arb_add_error(acb_realref(err->coeffs + i), T->coeffs + i);
if (!is_real)
arb_add_error(acb_imagref(err->coeffs + i), T->coeffs + i);
}
_acb_poly_set_length(err, len);
_acb_poly_normalise(err);
acb_poly_add(s, s, err, prec);
}
acb_poly_set(res, s);
acb_poly_clear(s);
acb_poly_clear(t);
acb_poly_clear(err);
arb_poly_clear(C);
arb_poly_clear(T);
}
