void mag_geom_series(mag_t res, const mag_t x, ulong n) { if (mag_is_zero(x)) { if (n == 0) mag_one(res); else mag_zero(res); } else if (mag_is_inf(x)) { mag_inf(res); } else { mag_t t; mag_init(t); mag_one(t); mag_sub_lower(t, t, x); if (mag_is_zero(t)) { mag_inf(res); } else { mag_pow_ui(res, x, n); mag_div(res, res, t); } mag_clear(t); } }
/* bound (1 + 1/m)^n, m > 0, n >= 0 */ void mag_binpow_uiui(mag_t b, ulong m, ulong n) { mag_t t; if (m == 0) { mag_inf(b); return; } mag_init(t); /* bound by exp(n/m) <= 1 + (n/m) + (n/m)^2 */ if (m > n) { mag_set_ui(t, n); /* x = n/m */ mag_div_ui(t, t, m); mag_mul(b, t, t); /* x^2 */ mag_add(b, b, t); /* x */ mag_one(t); mag_add(b, b, t); /* 1 */ } else { mag_one(b); mag_div_ui(b, b, m); mag_one(t); mag_add(t, t, b); mag_pow_ui(b, t, n); } mag_clear(t); }
static void acb_log1p_tiny(acb_t r, const acb_t z, slong prec) { mag_t b, c; acb_t t; int real; mag_init(b); mag_init(c); acb_init(t); real = acb_is_real(z); /* if |z| < 1, then |log(1+z) - [z - z^2/2]| <= |z|^3/(1-|z|) */ acb_get_mag(b, z); mag_one(c); mag_sub_lower(c, c, b); mag_pow_ui(b, b, 3); mag_div(b, b, c); acb_mul(t, z, z, prec); acb_mul_2exp_si(t, t, -1); acb_sub(r, z, t, prec); if (real && mag_is_finite(b)) arb_add_error_mag(acb_realref(r), b); else acb_add_error_mag(r, b); mag_clear(b); mag_clear(c); acb_clear(t); }
void mag_exp_tail(mag_t z, const mag_t x, ulong N) { if (N == 0 || mag_is_inf(x)) { mag_exp(z, x); } else if (mag_is_zero(x)) { mag_zero(z); } else { mag_t t; mag_init(t); mag_set_ui_2exp_si(t, N, -1); /* bound by geometric series when N >= 2*x <=> N/2 >= x */ if (mag_cmp(t, x) >= 0) { /* 2 c^N / N! */ mag_pow_ui(t, x, N); mag_rfac_ui(z, N); mag_mul(z, z, t); mag_mul_2exp_si(z, z, 1); } else { mag_exp(z, x); } mag_clear(t); } }
static void arb_sqrt1pm1_tiny(arb_t r, const arb_t z, slong prec) { mag_t b, c; arb_t t; mag_init(b); mag_init(c); arb_init(t); /* if |z| < 1, then |(sqrt(1+z)-1) - (z/2-z^2/8)| <= |z|^3/(1-|z|)/16 */ arb_get_mag(b, z); mag_one(c); mag_sub_lower(c, c, b); mag_pow_ui(b, b, 3); mag_div(b, b, c); mag_mul_2exp_si(b, b, -4); arb_mul(t, z, z, prec); arb_mul_2exp_si(t, t, -2); arb_sub(r, z, t, prec); arb_mul_2exp_si(r, r, -1); if (mag_is_finite(b)) arb_add_error_mag(r, b); else arb_indeterminate(r); mag_clear(b); mag_clear(c); arb_clear(t); }
static void acb_hypgeom_mag_Cn(mag_t Cn, int R, const mag_t nu, const mag_t sigma, ulong n) { if (R == 1) { mag_one(Cn); } else { acb_hypgeom_mag_chi(Cn, n); if (R == 3) { mag_t tmp; mag_init(tmp); mag_mul(tmp, nu, nu); mag_mul(tmp, tmp, sigma); if (n != 1) mag_mul_ui(tmp, tmp, n); mag_add(Cn, Cn, tmp); mag_pow_ui(tmp, nu, n); mag_mul(Cn, Cn, tmp); mag_clear(tmp); } } }
/* The error for eta(s) is bounded by 3/(3+sqrt(8))^n */ void mag_borwein_error(mag_t err, slong n) { /* upper bound for 1/(3+sqrt(8)) */ mag_set_ui_2exp_si(err, 736899889, -32); mag_pow_ui(err, err, n); mag_mul_ui(err, err, 3); }
void mag_polylog_tail(mag_t u, const mag_t z, long sigma, ulong d, ulong N) { mag_t TN, UN, t; if (N < 2) { mag_inf(u); return; } mag_init(TN); mag_init(UN); mag_init(t); if (mag_cmp_2exp_si(z, 0) >= 0) { mag_inf(u); } else { /* Bound T(N) */ mag_pow_ui(TN, z, N); /* multiply by log(N)^d */ if (d > 0) { mag_log_ui(t, N); mag_pow_ui(t, t, d); mag_mul(TN, TN, t); } /* multiply by 1/k^s */ if (sigma > 0) { mag_set_ui_lower(t, N); mag_pow_ui_lower(t, t, sigma); mag_div(TN, TN, t); } else if (sigma < 0) { mag_set_ui(t, N); mag_pow_ui(t, t, -sigma); mag_mul(TN, TN, t); } /* Bound U(N) */ mag_set(UN, z); /* multiply by (1 + 1/N)**S */ if (sigma < 0) { mag_binpow_uiui(t, N, -sigma); mag_mul(UN, UN, t); } /* multiply by (1 + 1/(N log(N)))^d */ if (d > 0) { ulong nl; /* rounds down */ nl = mag_d_log_lower_bound(N) * N * (1 - 1e-13); mag_binpow_uiui(t, nl, d); mag_mul(UN, UN, t); } /* T(N) / (1 - U(N)) */ if (mag_cmp_2exp_si(UN, 0) >= 0) { mag_inf(u); } else { mag_one(t); mag_sub_lower(t, t, UN); mag_div(u, TN, t); } } mag_clear(TN); mag_clear(UN); mag_clear(t); }
/* Given T(K), compute bound for T(n) z^n. We need to multiply by z^n * 1/rf(K+1,m)^r * (rf(K+1,m)/rf(K+1-A,m)) * (rf(K+1-B,m)/rf(K+1-2B,m)) where m = n - K. This is equal to z^n * (K+A)! (K-2B)! (K-B+m)! ----------------------- * ((K+m)! / K!)^(1-r) (K-B)! (K-A+m)! (K-2B+m)! */ void hypgeom_term_bound(mag_t Tn, const mag_t TK, slong K, slong A, slong B, int r, const mag_t z, slong n) { mag_t t, u, num; slong m; mag_init(t); mag_init(u); mag_init(num); m = n - K; if (m < 0) { flint_printf("hypgeom term bound\n"); abort(); } /* TK * z^n */ mag_pow_ui(t, z, n); mag_mul(num, TK, t); /* numerator: (K+A)! (K-2B)! (K-B+m)! */ mag_fac_ui(t, K+A); mag_mul(num, num, t); mag_fac_ui(t, K-2*B); mag_mul(num, num, t); mag_fac_ui(t, K-B+m); mag_mul(num, num, t); /* denominator: (K-B)! (K-A+m)! (K-2B+m)! */ mag_rfac_ui(t, K-B); mag_mul(num, num, t); mag_rfac_ui(t, K-A+m); mag_mul(num, num, t); mag_rfac_ui(t, K-2*B+m); mag_mul(num, num, t); /* ((K+m)! / K!)^(1-r) */ if (r == 0) { mag_fac_ui(t, K+m); mag_mul(num, num, t); mag_rfac_ui(t, K); mag_mul(num, num, t); } else if (r != 1) { mag_fac_ui(t, K); mag_rfac_ui(u, K+m); mag_mul(t, t, u); mag_pow_ui(t, t, r-1); mag_mul(num, num, t); } mag_set(Tn, num); mag_clear(t); mag_clear(u); mag_clear(num); }
void acb_hypgeom_pfq_sum_rs(acb_t res, acb_t term, acb_srcptr a, slong p, acb_srcptr b, slong q, const acb_t z, slong n, slong prec) { acb_ptr zpow; acb_t s, t, u; slong i, j, k, m; mag_t B, C; if (n == 0) { acb_zero(res); acb_one(term); return; } if (n < 0) abort(); m = n_sqrt(n); m = FLINT_MIN(m, 150); mag_init(B); mag_init(C); acb_init(s); acb_init(t); acb_init(u); zpow = _acb_vec_init(m + 1); _acb_vec_set_powers(zpow, z, m + 1, prec); mag_one(B); for (k = n; k >= 0; k--) { j = k % m; if (k < n) acb_add(s, s, zpow + j, prec); if (k > 0) { if (p > 0) { acb_add_ui(u, a, k - 1, prec); for (i = 1; i < p; i++) { acb_add_ui(t, a + i, k - 1, prec); acb_mul(u, u, t, prec); } if (k < n) acb_mul(s, s, u, prec); acb_get_mag(C, u); mag_mul(B, B, C); } if (q > 0) { acb_add_ui(u, b, k - 1, prec); for (i = 1; i < q; i++) { acb_add_ui(t, b + i, k - 1, prec); acb_mul(u, u, t, prec); } if (k < n) acb_div(s, s, u, prec); acb_get_mag_lower(C, u); mag_div(B, B, C); } if (j == 0 && k < n) { acb_mul(s, s, zpow + m, prec); } } } acb_get_mag(C, z); mag_pow_ui(C, C, n); mag_mul(B, B, C); acb_zero(term); if (_acb_vec_is_real(a, p) && _acb_vec_is_real(b, q) && acb_is_real(z)) arb_add_error_mag(acb_realref(term), B); else acb_add_error_mag(term, B); acb_set(res, s); mag_clear(B); mag_clear(C); acb_clear(s); acb_clear(t); acb_clear(u); _acb_vec_clear(zpow, m + 1); }
int acb_calc_integrate_taylor(acb_t res, acb_calc_func_t func, void * param, const acb_t a, const acb_t b, const arf_t inner_radius, const arf_t outer_radius, long accuracy_goal, long prec) { long num_steps, step, N, bp; int result; acb_t delta, m, x, y1, y2, sum; acb_ptr taylor_poly; arf_t err; acb_init(delta); acb_init(m); acb_init(x); acb_init(y1); acb_init(y2); acb_init(sum); arf_init(err); acb_sub(delta, b, a, prec); /* precision used for bounds calculations */ bp = MAG_BITS; /* compute the number of steps */ { arf_t t; arf_init(t); acb_get_abs_ubound_arf(t, delta, bp); arf_div(t, t, inner_radius, bp, ARF_RND_UP); arf_mul_2exp_si(t, t, -1); num_steps = (long) (arf_get_d(t, ARF_RND_UP) + 1.0); /* make sure it's not something absurd */ num_steps = FLINT_MIN(num_steps, 10 * prec); num_steps = FLINT_MAX(num_steps, 1); arf_clear(t); } result = ARB_CALC_SUCCESS; acb_zero(sum); for (step = 0; step < num_steps; step++) { /* midpoint of subinterval */ acb_mul_ui(m, delta, 2 * step + 1, prec); acb_div_ui(m, m, 2 * num_steps, prec); acb_add(m, m, a, prec); if (arb_calc_verbose) { printf("integration point %ld/%ld: ", 2 * step + 1, 2 * num_steps); acb_printd(m, 15); printf("\n"); } /* evaluate at +/- x */ /* TODO: exactify m, and include error in x? */ acb_div_ui(x, delta, 2 * num_steps, prec); /* compute bounds and number of terms to use */ { arb_t cbound, xbound, rbound; arf_t C, D, R, X, T; double DD, TT, NN; arb_init(cbound); arb_init(xbound); arb_init(rbound); arf_init(C); arf_init(D); arf_init(R); arf_init(X); arf_init(T); /* R is the outer radius */ arf_set(R, outer_radius); /* X = upper bound for |x| */ acb_get_abs_ubound_arf(X, x, bp); arb_set_arf(xbound, X); /* Compute C(m,R). Important subtlety: due to rounding when computing m, we will in general be farther than R away from the integration path. But since acb_calc_cauchy_bound actually integrates over the area traced by a complex interval, it will catch any extra singularities (giving an infinite bound). */ arb_set_arf(rbound, outer_radius); acb_calc_cauchy_bound(cbound, func, param, m, rbound, 8, bp); arf_set_mag(C, arb_radref(cbound)); arf_add(C, arb_midref(cbound), C, bp, ARF_RND_UP); /* Sanity check: we need C < inf and R > X */ if (arf_is_finite(C) && arf_cmp(R, X) > 0) { /* Compute upper bound for D = C * R * X / (R - X) */ arf_mul(D, C, R, bp, ARF_RND_UP); arf_mul(D, D, X, bp, ARF_RND_UP); arf_sub(T, R, X, bp, ARF_RND_DOWN); arf_div(D, D, T, bp, ARF_RND_UP); /* Compute upper bound for T = (X / R) */ arf_div(T, X, R, bp, ARF_RND_UP); /* Choose N */ /* TODO: use arf arithmetic to avoid overflow */ /* TODO: use relative accuracy (look at |f(m)|?) */ DD = arf_get_d(D, ARF_RND_UP); TT = arf_get_d(T, ARF_RND_UP); NN = -(accuracy_goal * 0.69314718055994530942 + log(DD)) / log(TT); N = NN + 0.5; N = FLINT_MIN(N, 100 * prec); N = FLINT_MAX(N, 1); /* Tail bound: D / (N + 1) * T^N */ { mag_t TT; mag_init(TT); arf_get_mag(TT, T); mag_pow_ui(TT, TT, N); arf_set_mag(T, TT); mag_clear(TT); } arf_mul(D, D, T, bp, ARF_RND_UP); arf_div_ui(err, D, N + 1, bp, ARF_RND_UP); } else { N = 1; arf_pos_inf(err); result = ARB_CALC_NO_CONVERGENCE; } if (arb_calc_verbose) { printf("N = %ld; bound: ", N); arf_printd(err, 15); printf("\n"); printf("R: "); arf_printd(R, 15); printf("\n"); printf("C: "); arf_printd(C, 15); printf("\n"); printf("X: "); arf_printd(X, 15); printf("\n"); } arb_clear(cbound); arb_clear(xbound); arb_clear(rbound); arf_clear(C); arf_clear(D); arf_clear(R); arf_clear(X); arf_clear(T); } /* evaluate Taylor polynomial */ taylor_poly = _acb_vec_init(N + 1); func(taylor_poly, m, param, N, prec); _acb_poly_integral(taylor_poly, taylor_poly, N + 1, prec); _acb_poly_evaluate(y2, taylor_poly, N + 1, x, prec); acb_neg(x, x); _acb_poly_evaluate(y1, taylor_poly, N + 1, x, prec); acb_neg(x, x); /* add truncation error */ arb_add_error_arf(acb_realref(y1), err); arb_add_error_arf(acb_imagref(y1), err); arb_add_error_arf(acb_realref(y2), err); arb_add_error_arf(acb_imagref(y2), err); acb_add(sum, sum, y2, prec); acb_sub(sum, sum, y1, prec); if (arb_calc_verbose) { printf("values: "); acb_printd(y1, 15); printf(" "); acb_printd(y2, 15); printf("\n"); } _acb_vec_clear(taylor_poly, N + 1); if (result == ARB_CALC_NO_CONVERGENCE) break; } acb_set(res, sum); acb_clear(delta); acb_clear(m); acb_clear(x); acb_clear(y1); acb_clear(y2); acb_clear(sum); arf_clear(err); return result; }