void
acb_lambertw_initial_asymp(acb_t w, const acb_t z, const fmpz_t k, slong prec)
{
acb_t L1, L2, t;
acb_init(L1);
acb_init(L2);
acb_init(t);
acb_const_pi(L2, prec);
acb_mul_2exp_si(L2, L2, 1);
acb_mul_fmpz(L2, L2, k, prec);
acb_mul_onei(L2, L2);
acb_log(L1, z, prec);
acb_add(L1, L1, L2, prec);
acb_log(L2, L1, prec);
/* L1 - L2 + L2/L1 + L2(L2-2)/(2 L1^2) */
acb_inv(t, L1, prec);
acb_mul_2exp_si(w, L2, 1);
acb_submul(w, L2, L2, prec);
acb_neg(w, w);
acb_mul(w, w, t, prec);
acb_mul_2exp_si(w, w, -1);
acb_add(w, w, L2, prec);
acb_mul(w, w, t, prec);
acb_sub(w, w, L2, prec);
acb_add(w, w, L1, prec);
acb_clear(L1);
acb_clear(L2);
acb_clear(t);
}
void
acb_log1p(acb_t r, const acb_t z, slong prec)
{
slong magz, magx, magy;
if (acb_is_zero(z))
{
acb_zero(r);
return;
}
magx = arf_abs_bound_lt_2exp_si(arb_midref(acb_realref(z)));
magy = arf_abs_bound_lt_2exp_si(arb_midref(acb_imagref(z)));
magz = FLINT_MAX(magx, magy);
if (magz < -prec)
{
acb_log1p_tiny(r, z, prec);
}
else
{
if (magz < 0)
acb_add_ui(r, z, 1, prec + (-magz) + 4);
else
acb_add_ui(r, z, 1, prec + 4);
acb_log(r, r, prec);
}
}
void
acb_lgamma(acb_t y, const acb_t x, long prec)
{
int reflect;
long r, n, wp;
acb_t t, u;
wp = prec + FLINT_BIT_COUNT(prec);
acb_gamma_stirling_choose_param(&reflect, &r, &n, x, 0, 0, wp);
/* log(gamma(x)) = log(gamma(x+r)) - log(rf(x,r)) */
acb_init(t);
acb_init(u);
acb_add_ui(t, x, r, wp);
acb_gamma_stirling_eval(u, t, n, 0, wp);
acb_rising_ui_rec(t, x, r, prec);
acb_log(t, t, prec);
_acb_log_rising_correct_branch(t, t, x, r, wp);
acb_sub(y, u, t, prec);
acb_clear(t);
acb_clear(u);
}
void
_acb_pow_arb_exp(acb_t z, const acb_t x, const arb_t y, long prec)
{
acb_t t;
acb_init(t);
acb_log(t, x, prec);
acb_mul_arb(t, t, y, prec);
acb_exp(z, t, prec);
acb_clear(t);
}
static void
_acb_hypgeom_li(acb_t res, const acb_t z, long prec)
{
if (acb_is_zero(z))
{
acb_zero(res);
}
else
{
acb_log(res, z, prec);
acb_hypgeom_ei(res, res, prec);
}
}
void
acb_acosh(acb_t res, const acb_t z, slong prec)
{
if (acb_is_one(z))
{
acb_zero(res);
}
else
{
acb_t t, u;
acb_init(t);
acb_init(u);
acb_add_ui(t, z, 1, prec);
acb_sub_ui(u, z, 1, prec);
acb_sqrt(t, t, prec);
acb_sqrt(u, u, prec);
acb_mul(t, t, u, prec);
acb_add(t, t, z, prec);
if (!arb_is_zero(acb_imagref(z)))
{
acb_log(res, t, prec);
}
else
{
/* pure imaginary on (-1,1) */
arb_abs(acb_realref(u), acb_realref(z));
arb_one(acb_imagref(u));
acb_log(res, t, prec);
if (arb_lt(acb_realref(u), acb_imagref(u)))
arb_zero(acb_realref(res));
}
acb_clear(t);
acb_clear(u);
}
}
/* f(z) = -log(z) / (1 + z) */
int
f_log_div1p(acb_ptr res, const acb_t z, void * param, slong order, slong prec)
{
acb_t t;
if (order > 1)
flint_abort(); /* Would be needed for Taylor method. */
acb_init(t);
acb_add_ui(t, z, 1, prec);
acb_log(res, z, prec);
acb_div(res, res, t, prec);
acb_neg(res, res);
acb_clear(t);
return 0;
}
void
acb_hypgeom_ci_2f3(acb_t res, const acb_t z, slong prec)
{
acb_t a, t, u;
acb_struct b[3];
acb_init(a);
acb_init(b);
acb_init(b + 1);
acb_init(b + 2);
acb_init(t);
acb_init(u);
acb_one(a);
acb_set_ui(b, 2);
acb_set(b + 1, b);
acb_set_ui(b + 2, 3);
acb_mul_2exp_si(b + 2, b + 2, -1);
acb_mul(t, z, z, prec);
acb_mul_2exp_si(t, t, -2);
acb_neg(t, t);
acb_hypgeom_pfq_direct(u, a, 1, b, 3, t, -1, prec);
acb_mul(u, u, t, prec);
acb_log(t, z, prec);
acb_add(u, u, t, prec);
arb_const_euler(acb_realref(t), prec);
arb_add(acb_realref(u), acb_realref(u), acb_realref(t), prec);
acb_swap(res, u);
acb_clear(a);
acb_clear(b);
acb_clear(b + 1);
acb_clear(b + 2);
acb_clear(t);
acb_clear(u);
}
/* todo: use log(1-z) when this is better? would also need to
adjust strategy in the main function */
void
acb_hypgeom_dilog_bernoulli(acb_t res, const acb_t z, slong prec)
{
acb_t s, w, w2;
slong n, k;
fmpz_t c, d;
mag_t m, err;
double lm;
int real;
acb_init(s);
acb_init(w);
acb_init(w2);
fmpz_init(c);
fmpz_init(d);
mag_init(m);
mag_init(err);
real = 0;
if (acb_is_real(z))
{
arb_sub_ui(acb_realref(w), acb_realref(z), 1, 30);
real = arb_is_nonpositive(acb_realref(w));
}
acb_log(w, z, prec);
acb_get_mag(m, w);
/* for k >= 4, the terms are bounded by (|w| / (2 pi))^k */
mag_set_ui_2exp_si(err, 2670177, -24); /* upper bound for 1/(2pi) */
mag_mul(err, err, m);
lm = mag_get_d_log2_approx(err);
if (lm < -0.25)
{
n = prec / (-lm) + 1;
n = FLINT_MAX(n, 4);
mag_geom_series(err, err, n);
BERNOULLI_ENSURE_CACHED(n)
acb_mul(w2, w, w, prec);
for (k = n - (n % 2 == 0); k >= 3; k -= 2)
{
fmpz_mul_ui(c, fmpq_denref(bernoulli_cache + k - 1), k - 1);
fmpz_mul_ui(d, c, (k + 1) * (k + 2));
acb_mul(s, s, w2, prec);
acb_mul_fmpz(s, s, c, prec);
fmpz_mul_ui(c, fmpq_numref(bernoulli_cache + k - 1), (k + 1) * (k + 2));
acb_sub_fmpz(s, s, c, prec);
acb_div_fmpz(s, s, d, prec);
}
acb_mul(s, s, w, prec);
acb_mul_2exp_si(s, s, 1);
acb_sub_ui(s, s, 3, prec);
acb_mul(s, s, w2, prec);
acb_mul_2exp_si(s, s, -1);
acb_const_pi(w2, prec);
acb_addmul(s, w2, w2, prec);
acb_div_ui(s, s, 6, prec);
acb_neg(w2, w);
acb_log(w2, w2, prec);
acb_submul(s, w2, w, prec);
acb_add(res, s, w, prec);
acb_add_error_mag(res, err);
if (real)
arb_zero(acb_imagref(res));
}
else
{
acb_indeterminate(res);
}
acb_clear(s);
acb_clear(w);
acb_clear(w2);
fmpz_clear(c);
fmpz_clear(d);
mag_clear(m);
mag_clear(err);
}
int main()
{
long iter;
flint_rand_t state;
printf("log....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 10000; iter++)
{
acb_t x, a, b;
long prec1, prec2;
prec1 = 2 + n_randint(state, 1000);
prec2 = prec1 + 30;
acb_init(x);
acb_init(a);
acb_init(b);
acb_randtest_special(x, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_randtest_special(a, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_randtest_special(b, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_log(a, x, prec1);
acb_log(b, x, prec2);
/* check consistency */
if (!acb_overlaps(a, b))
{
printf("FAIL: overlap\n\n");
printf("x = "); acb_printd(x, 15); printf("\n\n");
printf("a = "); acb_printd(a, 15); printf("\n\n");
printf("b = "); acb_printd(b, 15); printf("\n\n");
abort();
}
/* check exp(log(x)) = x */
acb_exp(b, b, prec1);
if (!acb_contains(b, x))
{
printf("FAIL: functional equation\n\n");
printf("x = "); acb_printd(x, 15); printf("\n\n");
printf("b = "); acb_printd(b, 15); printf("\n\n");
abort();
}
acb_log(x, x, prec1);
if (!acb_overlaps(a, x))
{
printf("FAIL: aliasing\n\n");
printf("a = "); acb_printd(a, 15); printf("\n\n");
printf("x = "); acb_printd(x, 15); printf("\n\n");
abort();
}
acb_clear(x);
acb_clear(a);
acb_clear(b);
}
flint_randclear(state);
flint_cleanup();
printf("PASS\n");
return EXIT_SUCCESS;
}
void
_acb_poly_lgamma_series(acb_ptr res, acb_srcptr h, slong hlen, slong len, slong prec)
{
int reflect;
slong i, r, n, wp;
acb_t zr;
acb_ptr t, u;
hlen = FLINT_MIN(hlen, len);
if (hlen == 1)
{
acb_lgamma(res, h, prec);
if (acb_is_finite(res))
_acb_vec_zero(res + 1, len - 1);
else
_acb_vec_indeterminate(res + 1, len - 1);
return;
}
if (len == 2)
{
acb_t v;
acb_init(v);
acb_set(v, h + 1);
acb_digamma(res + 1, h, prec);
acb_lgamma(res, h, prec);
acb_mul(res + 1, res + 1, v, prec);
acb_clear(v);
return;
}
/* use real code for real input and output */
if (_acb_vec_is_real(h, hlen) && arb_is_positive(acb_realref(h)))
{
arb_ptr tmp = _arb_vec_init(len);
for (i = 0; i < hlen; i++)
arb_set(tmp + i, acb_realref(h + i));
_arb_poly_lgamma_series(tmp, tmp, hlen, len, prec);
for (i = 0; i < len; i++)
acb_set_arb(res + i, tmp + i);
_arb_vec_clear(tmp, len);
return;
}
wp = prec + FLINT_BIT_COUNT(prec);
t = _acb_vec_init(len);
u = _acb_vec_init(len);
acb_init(zr);
/* use Stirling series */
acb_gamma_stirling_choose_param(&reflect, &r, &n, h, 1, 0, wp);
if (reflect)
{
/* log gamma(h+x) = log rf(1-(h+x), r) - log gamma(1-(h+x)+r) - log sin(pi (h+x)) + log(pi) */
if (r != 0) /* otherwise t = 0 */
{
acb_sub_ui(u, h, 1, wp);
acb_neg(u, u);
_log_rising_ui_series(t, u, r, len, wp);
for (i = 1; i < len; i += 2)
acb_neg(t + i, t + i);
}
acb_sub_ui(u, h, 1, wp);
acb_neg(u, u);
acb_add_ui(zr, u, r, wp);
_acb_poly_gamma_stirling_eval(u, zr, n, len, wp);
for (i = 1; i < len; i += 2)
acb_neg(u + i, u + i);
_acb_vec_sub(t, t, u, len, wp);
/* log(sin) is unstable with large imaginary parts;
cot_pi is implemented in a numerically stable way */
acb_set(u, h);
acb_one(u + 1);
_acb_poly_cot_pi_series(u, u, 2, len - 1, wp);
_acb_poly_integral(u, u, len, wp);
acb_const_pi(u, wp);
_acb_vec_scalar_mul(u + 1, u + 1, len - 1, u, wp);
acb_log_sin_pi(u, h, wp);
_acb_vec_sub(u, t, u, len, wp);
acb_const_pi(t, wp); /* todo: constant for log pi */
acb_log(t, t, wp);
acb_add(u, u, t, wp);
}
else
{
/* log gamma(x) = log gamma(x+r) - log rf(x,r) */
acb_add_ui(zr, h, r, wp);
_acb_poly_gamma_stirling_eval(u, zr, n, len, wp);
if (r != 0)
{
_log_rising_ui_series(t, h, r, len, wp);
_acb_vec_sub(u, u, t, len, wp);
}
}
/* compose with nonconstant part */
acb_zero(t);
_acb_vec_set(t + 1, h + 1, hlen - 1);
_acb_poly_compose_series(res, u, len, t, hlen, len, prec);
acb_clear(zr);
_acb_vec_clear(t, len);
_acb_vec_clear(u, len);
}
int main()
{
slong iter;
flint_rand_t state;
flint_printf("log1p....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 10000; iter++)
{
acb_t x, a, b;
slong prec1, prec2;
prec1 = 2 + n_randint(state, 1000);
prec2 = 2 + n_randint(state, 1000);
acb_init(x);
acb_init(a);
acb_init(b);
acb_randtest_special(x, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_randtest_special(a, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_randtest_special(b, state, 1 + n_randint(state, 1000), 2 + n_randint(state, 100));
acb_log1p(a, x, prec1);
acb_log1p(b, x, prec2);
/* check consistency */
if (!acb_overlaps(a, b))
{
flint_printf("FAIL: overlap\n\n");
flint_printf("x = "); acb_printd(x, 15); flint_printf("\n\n");
flint_printf("a = "); acb_printd(a, 15); flint_printf("\n\n");
flint_printf("b = "); acb_printd(b, 15); flint_printf("\n\n");
abort();
}
/* check log1p(x) = log(1+x) */
acb_add_ui(b, x, 1, prec2);
acb_log(b, b, prec2);
if (!acb_overlaps(a, b))
{
flint_printf("FAIL: log1p vs log\n\n");
flint_printf("x = "); acb_printd(x, 15); flint_printf("\n\n");
flint_printf("a = "); acb_printd(a, 15); flint_printf("\n\n");
flint_printf("b = "); acb_printd(b, 15); flint_printf("\n\n");
abort();
}
acb_log1p(x, x, prec1);
if (!acb_overlaps(a, x))
{
flint_printf("FAIL: aliasing\n\n");
flint_printf("a = "); acb_printd(a, 15); flint_printf("\n\n");
flint_printf("x = "); acb_printd(x, 15); flint_printf("\n\n");
abort();
}
acb_clear(x);
acb_clear(a);
acb_clear(b);
}
flint_randclear(state);
flint_cleanup();
flint_printf("PASS\n");
return EXIT_SUCCESS;
}
int main()
{
long iter;
flint_rand_t state;
printf("lgamma....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 10000; iter++)
{
acb_t a, b, c;
long prec1, prec2;
prec1 = 2 + n_randint(state, 500);
prec2 = prec1 + 30;
acb_init(a);
acb_init(b);
acb_init(c);
arb_randtest_precise(acb_realref(a), state, 1 + n_randint(state, 1000), 1 + n_randint(state, 10));
arb_randtest_precise(acb_imagref(a), state, 1 + n_randint(state, 1000), 1 + n_randint(state, 10));
acb_lgamma(b, a, prec1);
if (n_randint(state, 4) == 0)
{
acb_randtest(c, state, 1 + n_randint(state, 1000), 1 + n_randint(state, 10));
acb_add(a, a, c, prec1);
acb_sub(a, a, c, prec1);
}
acb_lgamma(c, a, prec2);
if (!acb_overlaps(b, c))
{
printf("FAIL: overlap\n\n");
printf("a = "); acb_print(a); printf("\n\n");
printf("b = "); acb_print(b); printf("\n\n");
printf("c = "); acb_print(c); printf("\n\n");
abort();
}
/* check lgamma(z+1) = lgamma(z) + log(z) */
acb_log(c, a, prec1);
acb_add(b, b, c, prec1);
acb_add_ui(c, a, 1, prec1);
acb_lgamma(c, c, prec1);
if (!acb_overlaps(b, c))
{
printf("FAIL: functional equation\n\n");
printf("a = "); acb_print(a); printf("\n\n");
printf("b = "); acb_print(b); printf("\n\n");
printf("c = "); acb_print(c); printf("\n\n");
abort();
}
acb_clear(a);
acb_clear(b);
acb_clear(c);
}
flint_randclear(state);
flint_cleanup();
printf("PASS\n");
return EXIT_SUCCESS;
}
void
acb_gamma_stirling_eval(acb_t s, const acb_t z, long nterms, int digamma, long prec)
{
acb_t t, logz, zinv, zinv2;
arb_t b;
mag_t err;
long k, term_prec;
double z_mag, term_mag;
acb_init(t);
acb_init(logz);
acb_init(zinv);
acb_init(zinv2);
arb_init(b);
acb_log(logz, z, prec);
acb_inv(zinv, z, prec);
nterms = FLINT_MAX(nterms, 1);
acb_zero(s);
if (nterms > 1)
{
acb_mul(zinv2, zinv, zinv, prec);
z_mag = arf_get_d(arb_midref(acb_realref(logz)), ARF_RND_UP) * 1.44269504088896;
for (k = nterms - 1; k >= 1; k--)
{
term_mag = bernoulli_bound_2exp_si(2 * k);
term_mag -= (2 * k - 1) * z_mag;
term_prec = prec + term_mag;
term_prec = FLINT_MIN(term_prec, prec);
term_prec = FLINT_MAX(term_prec, 10);
arb_gamma_stirling_coeff(b, k, digamma, term_prec);
if (prec > 2000)
{
acb_set_round(t, zinv2, term_prec);
acb_mul(s, s, t, term_prec);
}
else
acb_mul(s, s, zinv2, term_prec);
arb_add(acb_realref(s), acb_realref(s), b, term_prec);
}
if (digamma)
acb_mul(s, s, zinv2, prec);
else
acb_mul(s, s, zinv, prec);
}
/* remainder bound */
mag_init(err);
acb_gamma_stirling_bound(err, z, digamma ? 1 : 0, 1, nterms);
mag_add(arb_radref(acb_realref(s)), arb_radref(acb_realref(s)), err);
mag_add(arb_radref(acb_imagref(s)), arb_radref(acb_imagref(s)), err);
mag_clear(err);
if (digamma)
{
acb_neg(s, s);
acb_mul_2exp_si(zinv, zinv, -1);
acb_sub(s, s, zinv, prec);
acb_add(s, s, logz, prec);
}
else
{
/* (z-0.5)*log(z) - z + log(2*pi)/2 */
arb_one(b);
arb_mul_2exp_si(b, b, -1);
arb_set(acb_imagref(t), acb_imagref(z));
arb_sub(acb_realref(t), acb_realref(z), b, prec);
acb_mul(t, logz, t, prec);
acb_add(s, s, t, prec);
acb_sub(s, s, z, prec);
arb_const_log_sqrt2pi(b, prec);
arb_add(acb_realref(s), acb_realref(s), b, prec);
}
acb_clear(t);
acb_clear(logz);
acb_clear(zinv);
acb_clear(zinv2);
arb_clear(b);
}
static void
acb_log_sin_pi_half(acb_t res, const acb_t z, slong prec, int upper)
{
acb_t t, u, zmid;
arf_t n;
arb_t pi;
acb_init(t);
acb_init(u);
acb_init(zmid);
arf_init(n);
arb_init(pi);
arf_set(arb_midref(acb_realref(zmid)), arb_midref(acb_realref(z)));
arf_set(arb_midref(acb_imagref(zmid)), arb_midref(acb_imagref(z)));
arf_floor(n, arb_midref(acb_realref(zmid)));
arb_sub_arf(acb_realref(zmid), acb_realref(zmid), n, prec);
arb_const_pi(pi, prec);
if (arf_cmpabs_2exp_si(arb_midref(acb_imagref(zmid)), 2) < 1)
{
acb_sin_pi(t, zmid, prec);
acb_log(t, t, prec);
}
else /* i*pi*(z-0.5) + log((1-exp(-2i*pi*z))/2) */
{
acb_mul_2exp_si(t, zmid, 1);
acb_neg(t, t);
if (upper)
acb_conj(t, t);
acb_exp_pi_i(t, t, prec);
acb_sub_ui(t, t, 1, prec);
acb_neg(t, t);
acb_mul_2exp_si(t, t, -1);
acb_log(t, t, prec);
acb_one(u);
acb_mul_2exp_si(u, u, -1);
acb_sub(u, zmid, u, prec);
if (upper)
acb_conj(u, u);
acb_mul_onei(u, u);
acb_addmul_arb(t, u, pi, prec);
if (upper)
acb_conj(t, t);
}
if (upper)
arb_submul_arf(acb_imagref(t), pi, n, prec);
else
arb_addmul_arf(acb_imagref(t), pi, n, prec);
/* propagated error bound from the derivative pi cot(pi z) */
if (!acb_is_exact(z))
{
mag_t zm, um;
mag_init(zm);
mag_init(um);
acb_cot_pi(u, z, prec);
acb_mul_arb(u, u, pi, prec);
mag_hypot(zm, arb_radref(acb_realref(z)), arb_radref(acb_imagref(z)));
acb_get_mag(um, u);
mag_mul(um, um, zm);
acb_add_error_mag(t, um);
mag_clear(zm);
mag_clear(um);
}
acb_set(res, t);
acb_clear(t);
acb_clear(u);
acb_clear(zmid);
arf_clear(n);
arb_clear(pi);
}
