void
acb_hypgeom_erf(acb_t res, const acb_t z, slong prec)
{
double x, y, absz2, logz;
slong prec2;
if (!acb_is_finite(z))
{
acb_indeterminate(res);
return;
}
if (acb_is_zero(z))
{
acb_zero(res);
return;
}
if ((arf_cmpabs_2exp_si(arb_midref(acb_realref(z)), 0) < 0 &&
arf_cmpabs_2exp_si(arb_midref(acb_imagref(z)), 0) < 0))
{
acb_hypgeom_erf_1f1a(res, z, prec);
return;
}
if ((arf_cmpabs_2exp_si(arb_midref(acb_realref(z)), 64) > 0 ||
arf_cmpabs_2exp_si(arb_midref(acb_imagref(z)), 64) > 0))
{
acb_hypgeom_erf_asymp(res, z, prec, prec);
return;
}
x = arf_get_d(arb_midref(acb_realref(z)), ARF_RND_DOWN);
y = arf_get_d(arb_midref(acb_imagref(z)), ARF_RND_DOWN);
absz2 = x * x + y * y;
logz = 0.5 * log(absz2);
if (logz - absz2 < -(prec + 8) * 0.69314718055994530942)
{
/* If the asymptotic term is small, we can
compute with reduced precision */
prec2 = FLINT_MIN(prec + 4 + (y*y - x*x - logz) * 1.4426950408889634074, (double) prec);
prec2 = FLINT_MAX(8, prec2);
prec2 = FLINT_MIN(prec2, prec);
acb_hypgeom_erf_asymp(res, z, prec, prec2);
}
else if (arf_cmpabs(arb_midref(acb_imagref(z)), arb_midref(acb_realref(z))) > 0)
{
acb_hypgeom_erf_1f1a(res, z, prec);
}
else
{
acb_hypgeom_erf_1f1b(res, z, prec);
}
}
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_erf(acb_t res, const acb_t z, slong prec)
{
double x, y, abs_z2, log_z, log_erf_z_asymp;
slong prec2, wp;
int more_imaginary;
if (!acb_is_finite(z))
{
acb_indeterminate(res);
return;
}
if (acb_is_zero(z))
{
acb_zero(res);
return;
}
if ((arf_cmpabs_2exp_si(arb_midref(acb_realref(z)), -64) < 0 &&
arf_cmpabs_2exp_si(arb_midref(acb_imagref(z)), -64) < 0))
{
acb_hypgeom_erf_1f1(res, z, prec, prec, 1);
return;
}
if ((arf_cmpabs_2exp_si(arb_midref(acb_realref(z)), 64) > 0 ||
arf_cmpabs_2exp_si(arb_midref(acb_imagref(z)), 64) > 0))
{
acb_hypgeom_erf_asymp(res, z, 0, prec, prec);
return;
}
x = arf_get_d(arb_midref(acb_realref(z)), ARF_RND_DOWN);
y = arf_get_d(arb_midref(acb_imagref(z)), ARF_RND_DOWN);
abs_z2 = x * x + y * y;
log_z = 0.5 * log(abs_z2);
/* estimate of log(erf(z)), disregarding csgn term */
log_erf_z_asymp = y*y - x*x - log_z;
if (log_z - abs_z2 < -(prec + 8) * 0.69314718055994530942)
{
/* If the asymptotic term is small, we can
compute with reduced precision. */
prec2 = FLINT_MIN(prec + 4 + log_erf_z_asymp * 1.4426950408889634074, (double) prec);
prec2 = FLINT_MAX(8, prec2);
prec2 = FLINT_MIN(prec2, prec);
acb_hypgeom_erf_asymp(res, z, 0, prec, prec2);
}
else
{
more_imaginary = arf_cmpabs(arb_midref(acb_imagref(z)),
arb_midref(acb_realref(z))) > 0;
/* Worst case: exp(|x|^2), computed: exp(x^2).
(x^2+y^2) - (x^2-y^2) = 2y^2, etc. */
if (more_imaginary)
wp = prec + FLINT_MAX(2 * x * x, 0.0) * 1.4426950408889634074 + 5;
else
wp = prec + FLINT_MAX(2 * y * y, 0.0) * 1.4426950408889634074 + 5;
acb_hypgeom_erf_1f1(res, z, prec, wp, more_imaginary);
}
}
int main()
{
slong iter;
flint_rand_t state;
flint_printf("erfc....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 10000 * arb_test_multiplier(); iter++)
{
acb_t a, b, c;
slong prec1, prec2, prec3, prec4;
prec1 = 2 + n_randint(state, 1000);
prec2 = 2 + n_randint(state, 1000);
prec3 = 2 + n_randint(state, 1000);
prec4 = 2 + n_randint(state, 1000);
acb_init(a);
acb_init(b);
acb_init(c);
acb_randtest_special(a, state, 1 + n_randint(state, 1000), 1 + n_randint(state, 100));
acb_randtest_special(b, state, 1 + n_randint(state, 1000), 1 + n_randint(state, 100));
acb_randtest_special(c, state, 1 + n_randint(state, 1000), 1 + n_randint(state, 100));
switch (n_randint(state, 4))
{
case 0:
acb_hypgeom_erf_asymp(b, a, 1, prec1, prec3);
break;
case 1:
acb_hypgeom_erf(b, a, prec1);
acb_sub_ui(b, b, 1, prec1);
acb_neg(b, b);
break;
default:
acb_hypgeom_erfc(b, a, prec1);
}
switch (n_randint(state, 4))
{
case 0:
acb_hypgeom_erf_asymp(c, a, 1, prec2, prec4);
break;
case 1:
acb_hypgeom_erf(c, a, prec2);
acb_sub_ui(c, c, 1, prec2);
acb_neg(c, c);
break;
default:
acb_hypgeom_erfc(c, a, prec2);
}
if (!acb_overlaps(b, c))
{
flint_printf("FAIL: overlap\n\n");
flint_printf("a = "); acb_printd(a, 30); flint_printf("\n\n");
flint_printf("b = "); acb_printd(b, 30); flint_printf("\n\n");
flint_printf("c = "); acb_printd(c, 30); flint_printf("\n\n");
abort();
}
acb_clear(a);
acb_clear(b);
acb_clear(c);
}
flint_randclear(state);
flint_cleanup();
flint_printf("PASS\n");
return EXIT_SUCCESS;
}
