void arb_poly_exp_series(arb_poly_t f, const arb_poly_t h, slong n, slong prec) { slong hlen = h->length; if (n == 0) { arb_poly_zero(f); return; } if (hlen == 0) { arb_poly_one(f); return; } if (hlen == 1) n = 1; arb_poly_fit_length(f, n); _arb_poly_exp_series(f->coeffs, h->coeffs, hlen, n, prec); _arb_poly_set_length(f, n); _arb_poly_normalise(f); }
void _arb_poly_sinh_cosh_series_exponential(arb_ptr s, arb_ptr c, const arb_srcptr h, slong hlen, slong len, slong prec) { arb_ptr t, u, v; arb_t s0, c0; hlen = FLINT_MIN(hlen, len); if (hlen == 1) { arb_sinh_cosh(s, c, h, prec); _arb_vec_zero(s + 1, len - 1); _arb_vec_zero(c + 1, len - 1); return; } arb_init(s0); arb_init(c0); t = _arb_vec_init(3 * len); u = t + len; v = u + len; arb_sinh_cosh(s0, c0, h, prec); _arb_vec_set(t + 1, h + 1, hlen - 1); _arb_poly_exp_series(t, t, len, len, prec); /* todo: part of the inverse could be avoided since exp computes it internally to half the length */ _arb_poly_inv_series(u, t, len, len, prec); /* hyperbolic sine */ _arb_vec_sub(s, t, u, len, prec); _arb_vec_scalar_mul_2exp_si(s, s, len, -1); /* hyperbolic cosine */ _arb_vec_add(c, t, u, len, prec); _arb_vec_scalar_mul_2exp_si(c, c, len, -1); /* sinh(h0 + h1) = cosh(h0) sinh(h1) + sinh(h0) cosh(h1) cosh(h0 + h1) = cosh(h0) cosh(h1) + sinh(h0) sinh(h1) */ if (!arb_is_zero(s0)) { _arb_vec_scalar_mul(t, s, len, c0, prec); _arb_vec_scalar_mul(u, c, len, s0, prec); _arb_vec_scalar_mul(v, s, len, s0, prec); _arb_vec_add(s, t, u, len, prec); _arb_vec_scalar_mul(t, c, len, c0, prec); _arb_vec_add(c, t, v, len, prec); } _arb_vec_clear(t, 3 * len); arb_clear(s0); arb_clear(c0); }
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); }
void _arb_bell_sum_taylor(arb_t res, const fmpz_t n, const fmpz_t a, const fmpz_t b, const fmpz_t mmag, long tol) { fmpz_t m, r, R, tmp; mag_t B, C, D, bound; arb_t t, u; long wp, k, N; if (_fmpz_sub_small(b, a) < 5) { arb_bell_sum_bsplit(res, n, a, b, mmag, tol); return; } fmpz_init(m); fmpz_init(r); fmpz_init(R); fmpz_init(tmp); /* r = max(m - a, b - m) */ /* m = a + (b - a) / 2 */ fmpz_sub(r, b, a); fmpz_cdiv_q_2exp(r, r, 1); fmpz_add(m, a, r); fmpz_mul_2exp(R, r, RADIUS_BITS); mag_init(B); mag_init(C); mag_init(D); mag_init(bound); arb_init(t); arb_init(u); if (fmpz_cmp(R, m) >= 0) { mag_inf(C); mag_inf(D); } else { /* C = exp(R * |F'(m)| + (1/2) R^2 * (n/(m-R)^2 + 1/(m-R))) */ /* C = exp(R * (|F'(m)| + (1/2) R * (n/(m-R) + 1)/(m-R))) */ /* D = (1/2) R * (n/(m-R) + 1)/(m-R) */ fmpz_sub(tmp, m, R); mag_set_fmpz(D, n); mag_div_fmpz(D, D, tmp); mag_one(C); mag_add(D, D, C); mag_div_fmpz(D, D, tmp); mag_mul_fmpz(D, D, R); mag_mul_2exp_si(D, D, -1); /* C = |F'(m)| */ wp = 20 + 1.05 * fmpz_bits(n); arb_set_fmpz(t, n); arb_div_fmpz(t, t, m, wp); fmpz_add_ui(tmp, m, 1); arb_set_fmpz(u, tmp); arb_digamma(u, u, wp); arb_sub(t, t, u, wp); arb_get_mag(C, t); /* C = exp(R * (C + D)) */ mag_add(C, C, D); mag_mul_fmpz(C, C, R); mag_exp(C, C); } if (mag_cmp_2exp_si(C, tol / 4 + 2) > 0) { _arb_bell_sum_taylor(res, n, a, m, mmag, tol); _arb_bell_sum_taylor(t, n, m, b, mmag, tol); arb_add(res, res, t, 2 * tol); } else { arb_ptr mx, ser1, ser2, ser3; /* D = T(m) */ wp = 20 + 1.05 * fmpz_bits(n); arb_set_fmpz(t, m); arb_pow_fmpz(t, t, n, wp); fmpz_add_ui(tmp, m, 1); arb_gamma_fmpz(u, tmp, wp); arb_div(t, t, u, wp); arb_get_mag(D, t); /* error bound: (b-a) * C * D * B^N / (1 - B), B = r/R */ /* ((b-a) * C * D * 2) * 2^(-N*RADIUS_BITS) */ /* ((b-a) * C * D * 2) */ mag_mul(bound, C, D); mag_mul_2exp_si(bound, bound, 1); fmpz_sub(tmp, b, a); mag_mul_fmpz(bound, bound, tmp); /* N = (tol + log2((b-a)*C*D*2) - mmag) / RADIUS_BITS */ if (mmag == NULL) { /* estimate D ~= 2^mmag */ fmpz_add_ui(tmp, MAG_EXPREF(C), tol); fmpz_cdiv_q_ui(tmp, tmp, RADIUS_BITS); } else { fmpz_sub(tmp, MAG_EXPREF(bound), mmag); fmpz_add_ui(tmp, tmp, tol); fmpz_cdiv_q_ui(tmp, tmp, RADIUS_BITS); } if (fmpz_cmp_ui(tmp, 5 * tol / 4) > 0) N = 5 * tol / 4; else if (fmpz_cmp_ui(tmp, 2) < 0) N = 2; else N = fmpz_get_ui(tmp); /* multiply by 2^(-N*RADIUS_BITS) */ mag_mul_2exp_si(bound, bound, -N * RADIUS_BITS); mx = _arb_vec_init(2); ser1 = _arb_vec_init(N); ser2 = _arb_vec_init(N); ser3 = _arb_vec_init(N); /* estimate (this should work for moderate n and tol) */ wp = 1.1 * tol + 1.05 * fmpz_bits(n) + 5; /* increase precision until convergence */ while (1) { /* (m+x)^n / gamma(m+1+x) */ arb_set_fmpz(mx, m); arb_one(mx + 1); _arb_poly_log_series(ser1, mx, 2, N, wp); for (k = 0; k < N; k++) arb_mul_fmpz(ser1 + k, ser1 + k, n, wp); arb_add_ui(mx, mx, 1, wp); _arb_poly_lgamma_series(ser2, mx, 2, N, wp); _arb_vec_sub(ser1, ser1, ser2, N, wp); _arb_poly_exp_series(ser3, ser1, N, N, wp); /* t = a - m, u = b - m */ arb_set_fmpz(t, a); arb_sub_fmpz(t, t, m, wp); arb_set_fmpz(u, b); arb_sub_fmpz(u, u, m, wp); arb_power_sum_vec(ser1, t, u, N, wp); arb_zero(res); for (k = 0; k < N; k++) arb_addmul(res, ser3 + k, ser1 + k, wp); if (mmag != NULL) { if (_fmpz_sub_small(MAG_EXPREF(arb_radref(res)), mmag) <= -tol) break; } else { if (arb_rel_accuracy_bits(res) >= tol) break; } wp = 2 * wp; } /* add the series truncation bound */ arb_add_error_mag(res, bound); _arb_vec_clear(mx, 2); _arb_vec_clear(ser1, N); _arb_vec_clear(ser2, N); _arb_vec_clear(ser3, N); } mag_clear(B); mag_clear(C); mag_clear(D); mag_clear(bound); arb_clear(t); arb_clear(u); fmpz_clear(m); fmpz_clear(r); fmpz_clear(R); fmpz_clear(tmp); }