void
acb_lambertw(acb_t res, const acb_t z, const fmpz_t k, int flags, slong prec)
{
acb_t ez1;
if (!acb_is_finite(z))
{
acb_indeterminate(res);
return;
}
if (flags == ACB_LAMBERTW_LEFT)
{
acb_lambertw_left(res, z, k, prec);
return;
}
if (flags == ACB_LAMBERTW_MIDDLE)
{
acb_lambertw_middle(res, z, prec);
return;
}
if (acb_contains_zero(z) && !fmpz_is_zero(k))
{
acb_indeterminate(res);
return;
}
acb_init(ez1);
/* precompute z*e + 1 */
arb_const_e(acb_realref(ez1), prec);
acb_mul(ez1, ez1, z, prec);
acb_add_ui(ez1, ez1, 1, prec);
/* Compute standard branches */
/* use real code when possible */
if (acb_is_real(z) && arb_is_positive(acb_realref(ez1)) &&
(fmpz_is_zero(k) ||
(fmpz_equal_si(k, -1) && arb_is_negative(acb_realref(z)))))
{
arb_lambertw(acb_realref(res), acb_realref(z), !fmpz_is_zero(k), prec);
arb_zero(acb_imagref(res));
}
else
{
_acb_lambertw(res, z, ez1, k, flags, prec);
}
acb_clear(ez1);
}
int main()
{
slong iter;
flint_rand_t state;
flint_printf("const_e....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 250 * arb_test_multiplier(); iter++)
{
arb_t r;
mpfr_t s;
slong accuracy, prec;
prec = 2 + n_randint(state, 1 << n_randint(state, 16));
arb_init(r);
mpfr_init2(s, prec + 1000);
arb_const_e(r, prec);
mpfr_set_ui(s, 1, MPFR_RNDN);
mpfr_exp(s, s, MPFR_RNDN);
if (!arb_contains_mpfr(r, s))
{
flint_printf("FAIL: containment\n\n");
flint_printf("prec = %wd\n", prec);
flint_printf("r = "); arb_printd(r, prec / 3.33); flint_printf("\n\n");
flint_abort();
}
accuracy = arb_rel_accuracy_bits(r);
if (accuracy < prec - 4)
{
flint_printf("FAIL: poor accuracy\n\n");
flint_printf("prec = %wd\n", prec);
flint_printf("r = "); arb_printd(r, prec / 3.33); flint_printf("\n\n");
flint_abort();
}
arb_clear(r);
mpfr_clear(s);
}
flint_randclear(state);
flint_cleanup();
flint_printf("PASS\n");
return EXIT_SUCCESS;
}
int
f_lambertw(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);
prec = FLINT_MIN(prec, acb_rel_accuracy_bits(z) + 10);
if (order != 0)
{
/* check for branch cut */
arb_const_e(acb_realref(t), prec);
acb_inv(t, t, prec);
acb_add(t, t, z, prec);
if (arb_contains_zero(acb_imagref(t)) &&
arb_contains_nonpositive(acb_realref(t)))
{
acb_indeterminate(t);
}
}
if (acb_is_finite(t))
{
fmpz_t k;
fmpz_init(k);
acb_lambertw(res, z, k, 0, prec);
fmpz_clear(k);
}
else
{
acb_indeterminate(res);
}
acb_clear(t);
return 0;
}
void
acb_lambertw_cleared_cut(acb_t res, const acb_t z, const fmpz_t k, int flags, slong prec)
{
acb_t ez1;
acb_init(ez1);
/* compute e*z + 1 */
arb_const_e(acb_realref(ez1), prec);
acb_mul(ez1, ez1, z, prec);
acb_add_ui(ez1, ez1, 1, prec);
if (acb_is_exact(z))
{
acb_lambertw_main(res, z, ez1, k, flags, prec);
}
else
{
acb_t zz;
mag_t err, rad;
mag_init(err);
mag_init(rad);
acb_init(zz);
acb_lambertw_bound_deriv(err, z, ez1, k);
mag_hypot(rad, arb_radref(acb_realref(z)), arb_radref(acb_imagref(z)));
mag_mul(err, err, rad);
acb_set(zz, z);
mag_zero(arb_radref(acb_realref(zz)));
mag_zero(arb_radref(acb_imagref(zz))); /* todo: recompute ez1? */
acb_lambertw_main(res, zz, ez1, k, flags, prec);
acb_add_error_mag(res, err);
mag_clear(err);
mag_clear(rad);
acb_clear(zz);
}
acb_clear(ez1);
}
int main()
{
long p = 1000;
long d = 53;
arb_t a, b, x, t;
arb_init(a);
arb_init(b);
arb_init(x);
arb_init(t);
// a = 1 + 2 ^ -76
arb_set_str(a, "2", p);
arb_set_str(t, "-76", p);
arb_pow(a, a, t, p);
arb_set_str(t, "1", p);
arb_add(a, t, a, p);
printf("a = "); arb_printd(a, d); printf("\n");
// b = 4 ^ 38 + 0.5
arb_set_str(b, "0.5", p);
arb_ui_pow_ui(t, 4, 38, p);
arb_add(b, t, b, p);
printf("b = "); arb_printd(b, d); printf("\n");
// x = a ^ b
arb_pow(x, a, b, p);
printf("x = "); arb_printd(x, d); printf("\n");
arb_const_e(t, p);
printf("e = "); arb_printd(t, d); printf("\n");
arb_sub(t, x, t, p);
printf("x-e = "); arb_printd(t, d); printf("\n");
printf("Computed with arb-%s\n", arb_version);
arb_clear(a);
arb_clear(b);
arb_clear(x);
arb_clear(t);
}
/* note: z should be exact here */
void acb_lambertw_main(acb_t res, const acb_t z,
const acb_t ez1, const fmpz_t k, int flags, slong prec)
{
acb_t w, t, oldw, ew;
mag_t err;
slong i, wp, accuracy, ebits, kbits, mbits, wp_initial, extraprec;
int have_ew;
acb_init(t);
acb_init(w);
acb_init(oldw);
acb_init(ew);
mag_init(err);
/* We need higher precision for large k, large exponents, or very close
to the branch point at -1/e. todo: we should be recomputing
ez1 to higher precision when close... */
acb_get_mag(err, z);
if (fmpz_is_zero(k) && mag_cmp_2exp_si(err, 0) < 0)
ebits = 0;
else
ebits = fmpz_bits(MAG_EXPREF(err));
if (fmpz_is_zero(k) || (fmpz_is_one(k) && arb_is_negative(acb_imagref(z)))
|| (fmpz_equal_si(k, -1) && arb_is_nonnegative(acb_imagref(z))))
{
acb_get_mag(err, ez1);
mbits = -MAG_EXP(err);
mbits = FLINT_MAX(mbits, 0);
mbits = FLINT_MIN(mbits, prec);
}
else
{
mbits = 0;
}
kbits = fmpz_bits(k);
extraprec = FLINT_MAX(ebits, kbits);
extraprec = FLINT_MAX(extraprec, mbits);
wp = wp_initial = 40 + extraprec;
accuracy = acb_lambertw_initial(w, z, ez1, k, wp_initial);
mag_zero(arb_radref(acb_realref(w)));
mag_zero(arb_radref(acb_imagref(w)));
/* We should be able to compute e^w for the final certification
during the Halley iteration. */
have_ew = 0;
for (i = 0; i < 5 + FLINT_BIT_COUNT(prec + extraprec); i++)
{
/* todo: should we restart? */
if (!acb_is_finite(w))
break;
wp = FLINT_MIN(3 * accuracy, 1.1 * prec + 10);
wp = FLINT_MAX(wp, 40);
wp += extraprec;
acb_set(oldw, w);
acb_lambertw_halley_step(t, ew, z, w, wp);
/* estimate the error (conservatively) */
acb_sub(w, w, t, wp);
acb_get_mag(err, w);
acb_set(w, t);
acb_add_error_mag(t, err);
accuracy = acb_rel_accuracy_bits(t);
if (accuracy > 2 * extraprec)
accuracy *= 2.9; /* less conservatively */
accuracy = FLINT_MIN(accuracy, wp);
accuracy = FLINT_MAX(accuracy, 0);
if (accuracy > prec + extraprec)
{
/* e^w = e^oldw * e^(w-oldw) */
acb_sub(t, w, oldw, wp);
acb_exp(t, t, wp);
acb_mul(ew, ew, t, wp);
have_ew = 1;
break;
}
mag_zero(arb_radref(acb_realref(w)));
mag_zero(arb_radref(acb_imagref(w)));
}
wp = FLINT_MIN(3 * accuracy, 1.1 * prec + 10);
wp = FLINT_MAX(wp, 40);
wp += extraprec;
if (acb_lambertw_check_branch(w, k, wp))
{
acb_t u, r, eu1;
mag_t err, rad;
acb_init(u);
acb_init(r);
acb_init(eu1);
mag_init(err);
mag_init(rad);
if (have_ew)
acb_set(t, ew);
else
acb_exp(t, w, wp);
/* t = w e^w */
acb_mul(t, t, w, wp);
acb_sub(r, t, z, wp);
/* Bound W' on the straight line path between t and z */
acb_union(u, t, z, wp);
arb_const_e(acb_realref(eu1), wp);
arb_zero(acb_imagref(eu1));
acb_mul(eu1, eu1, u, wp);
acb_add_ui(eu1, eu1, 1, wp);
if (acb_lambertw_branch_crossing(u, eu1, k))
{
mag_inf(err);
}
else
{
acb_lambertw_bound_deriv(err, u, eu1, k);
acb_get_mag(rad, r);
mag_mul(err, err, rad);
}
acb_add_error_mag(w, err);
acb_set(res, w);
acb_clear(u);
acb_clear(r);
acb_clear(eu1);
mag_clear(err);
mag_clear(rad);
}
else
{
acb_indeterminate(res);
}
acb_clear(t);
acb_clear(w);
acb_clear(oldw);
acb_clear(ew);
mag_clear(err);
}
