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);
}
}
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);
}
}
void
arb_div(arb_t z, const arb_t x, const arb_t y, long prec)
{
mag_t zr, xm, ym, yl, yw;
int inexact;
if (arb_is_exact(y))
{
arb_div_arf(z, x, arb_midref(y), prec);
}
else if (mag_is_inf(arb_radref(x)) || mag_is_inf(arb_radref(y)))
{
arf_div(arb_midref(z), arb_midref(x), arb_midref(y), prec, ARB_RND);
mag_inf(arb_radref(z));
}
else
{
mag_init_set_arf(xm, arb_midref(x));
mag_init_set_arf(ym, arb_midref(y));
mag_init(zr);
mag_init(yl);
mag_init(yw);
/* (|x|*yrad + |y|*xrad)/(y*(|y|-yrad)) */
mag_mul(zr, xm, arb_radref(y));
mag_addmul(zr, ym, arb_radref(x));
arb_get_mag_lower(yw, y);
arf_get_mag_lower(yl, arb_midref(y));
mag_mul_lower(yl, yl, yw);
mag_div(zr, zr, yl);
inexact = arf_div(arb_midref(z), arb_midref(x), arb_midref(y), prec, ARB_RND);
if (inexact)
arf_mag_add_ulp(arb_radref(z), zr, arb_midref(z), prec);
else
mag_swap(arb_radref(z), zr);
mag_clear(xm);
mag_clear(ym);
mag_clear(zr);
mag_clear(yl);
mag_clear(yw);
}
}
void
mag_expinv(mag_t res, const mag_t x)
{
if (mag_is_zero(x))
{
mag_one(res);
}
else if (mag_is_inf(x))
{
mag_zero(res);
}
else if (fmpz_sgn(MAG_EXPREF(x)) <= 0)
{
mag_one(res);
}
else if (fmpz_cmp_ui(MAG_EXPREF(x), 2 * MAG_BITS) > 0)
{
fmpz_t t;
fmpz_init(t);
/* If x > 2^60, exp(-x) < 2^(-2^60 / log(2)) */
/* -1/log(2) < -369/256 */
fmpz_set_si(t, -369);
fmpz_mul_2exp(t, t, 2 * MAG_BITS - 8);
mag_one(res);
mag_mul_2exp_fmpz(res, res, t);
fmpz_clear(t);
}
else
{
fmpz_t t;
slong e = MAG_EXP(x);
fmpz_init(t);
fmpz_set_ui(t, MAG_MAN(x));
if (e >= MAG_BITS)
fmpz_mul_2exp(t, t, e - MAG_BITS);
else
fmpz_tdiv_q_2exp(t, t, MAG_BITS - e);
/* upper bound for 1/e */
mag_set_ui_2exp_si(res, 395007543, -30);
mag_pow_fmpz(res, res, t);
fmpz_clear(t);
}
}
static void
arb_infimum(arf_t res, const arb_t x)
{
if (arf_is_nan(arb_midref(x)))
{
arf_nan(res);
}
else if (mag_is_inf(arb_radref(x)))
{
arf_neg_inf(res);
}
else
{
arf_set_mag(res, arb_radref(x));
arf_sub(res, arb_midref(x), res, ARF_PREC_EXACT, ARF_RND_FLOOR);
}
}
static void
arb_supremum(arf_t res, const arb_t x)
{
if (arf_is_nan(arb_midref(x)))
{
arf_nan(res);
}
else if (mag_is_inf(arb_radref(x)))
{
arf_pos_inf(res);
}
else
{
arf_set_mag(res, arb_radref(x));
arf_add(res, res, arb_midref(x), ARF_PREC_EXACT, ARF_RND_CEIL);
}
}
void
arb_div_arf(arb_t z, const arb_t x, const arf_t y, long prec)
{
mag_t zr, ym;
int inexact;
if (arf_is_zero(y))
{
arb_zero_pm_inf(z);
}
else if (arb_is_exact(x))
{
inexact = arf_div(arb_midref(z), arb_midref(x), y, prec, ARB_RND);
if (inexact)
arf_mag_set_ulp(arb_radref(z), arb_midref(z), prec);
else
mag_zero(arb_radref(z));
}
else if (mag_is_inf(arb_radref(x)))
{
arf_div(arb_midref(z), arb_midref(x), y, prec, ARB_RND);
mag_inf(arb_radref(z));
}
else
{
mag_init(ym);
mag_init(zr);
arf_get_mag_lower(ym, y);
mag_div(zr, arb_radref(x), ym);
inexact = arf_div(arb_midref(z), arb_midref(x), y, prec, ARB_RND);
if (inexact)
arf_mag_add_ulp(arb_radref(z), zr, arb_midref(z), prec);
else
mag_swap(arb_radref(z), zr);
mag_clear(ym);
mag_clear(zr);
}
}
double
mag_get_d(const mag_t z)
{
if (mag_is_zero(z))
{
return 0.0;
}
else if (mag_is_inf(z))
{
return D_INF;
}
else if (MAG_EXP(z) < -1000 || MAG_EXP(z) > 1000)
{
if (fmpz_sgn(MAG_EXPREF(z)) < 0)
return ldexp(1.0, -1000);
else
return D_INF;
}
else
{
return ldexp(MAG_MAN(z), MAG_EXP(z) - MAG_BITS);
}
}
void
mag_pow_ui_lower(mag_t z, const mag_t x, ulong e)
{
if (e <= 2)
{
if (e == 0)
mag_one(z);
else if (e == 1)
mag_set(z, x);
else
mag_mul_lower(z, x, x);
}
else if (mag_is_inf(x))
{
mag_inf(z);
}
else
{
mag_t y;
int i, bits;
mag_init_set(y, x);
bits = FLINT_BIT_COUNT(e);
for (i = bits - 2; i >= 0; i--)
{
mag_mul_lower(y, y, y);
if (e & (1UL << i))
mag_mul_lower(y, y, x);
}
mag_swap(z, y);
mag_clear(y);
}
}
void
acb_modular_theta_const_sum(acb_t theta2, acb_t theta3, acb_t theta4,
const acb_t q, long prec)
{
mag_t qmag, err;
double log2q_approx;
int is_real, is_real_or_imag;
long N;
mag_init(qmag);
mag_init(err);
acb_get_mag(qmag, q);
log2q_approx = mag_get_log2_d_approx(qmag);
is_real = arb_is_zero(acb_imagref(q));
is_real_or_imag = is_real || arb_is_zero(acb_realref(q));
if (log2q_approx >= 0.0)
{
N = 1;
mag_inf(err);
}
else
{
N = 0;
while (0.05 * N * N < prec)
{
if (log2q_approx * ((N+2)*(N+2)/4) < -prec - 2)
break;
N++;
}
N = (N+2)*(N+2)/4;
mag_geom_series(err, qmag, N);
mag_mul_2exp_si(err, err, 1); /* each term is taken twice */
if (mag_is_inf(err))
N = 1;
}
if (N < 1800)
acb_modular_theta_const_sum_basecase(theta2, theta3, theta4, q, N, prec);
else
acb_modular_theta_const_sum_rs(theta2, theta3, theta4, q, N, prec);
if (is_real_or_imag)
arb_add_error_mag(acb_realref(theta2), err);
else
acb_add_error_mag(theta2, err);
if (is_real)
{
arb_add_error_mag(acb_realref(theta3), err);
arb_add_error_mag(acb_realref(theta4), err);
}
else
{
acb_add_error_mag(theta3, err);
acb_add_error_mag(theta4, err);
}
mag_clear(qmag);
mag_clear(err);
}
void
acb_hypgeom_2f1_continuation(acb_t res, acb_t res1,
const acb_t a, const acb_t b, const acb_t c, const acb_t y,
const acb_t z, const acb_t f0, const acb_t f1, long prec)
{
mag_t A, nu, N, w, err, err1, R, T, goal;
acb_t x;
long j, k;
mag_init(A);
mag_init(nu);
mag_init(N);
mag_init(err);
mag_init(err1);
mag_init(w);
mag_init(R);
mag_init(T);
mag_init(goal);
acb_init(x);
bound(A, nu, N, a, b, c, y, f0, f1);
acb_sub(x, z, y, prec);
/* |T(k)| <= A * binomial(N+k, k) * nu^k * |x|^k */
acb_get_mag(w, x);
mag_mul(w, w, nu); /* w = nu |x| */
mag_mul_2exp_si(goal, A, -prec-2);
/* bound for T(0) */
mag_set(T, A);
mag_inf(R);
for (k = 1; k < 100 * prec; k++)
{
/* T(k) = T(k) * R(k), R(k) = (N+k)/k * w = (1 + N/k) w */
mag_div_ui(R, N, k);
mag_add_ui(R, R, 1);
mag_mul(R, R, w);
/* T(k) */
mag_mul(T, T, R);
if (mag_cmp(T, goal) <= 0 && mag_cmp_2exp_si(R, 0) < 0)
break;
}
/* T(k) [1 + R + R^2 + R^3 + ...] */
mag_geom_series(err, R, 0);
mag_mul(err, T, err);
/* Now compute T, R for the derivative */
/* Coefficients are A * (k+1) * binomial(N+k+1, k+1) */
mag_add_ui(T, N, 1);
mag_mul(T, T, A);
mag_inf(R);
for (j = 1; j <= k; j++)
{
mag_add_ui(R, N, k + 1);
mag_div_ui(R, R, k);
mag_mul(R, R, w);
mag_mul(T, T, R);
}
mag_geom_series(err1, R, 0);
mag_mul(err1, T, err1);
if (mag_is_inf(err))
{
acb_indeterminate(res);
acb_indeterminate(res1);
}
else
{
evaluate_sum(res, res1, a, b, c, y, x, f0, f1, k, prec);
acb_add_error_mag(res, err);
acb_add_error_mag(res1, err1);
}
mag_clear(A);
mag_clear(nu);
mag_clear(N);
mag_clear(err);
mag_clear(err1);
mag_clear(w);
mag_clear(R);
mag_clear(T);
mag_clear(goal);
acb_clear(x);
}
