def _log_ndtr_lower(x, series_order): """Asymptotic expansion version of `Log[cdf(x)]`, appropriate for `x<<-1`.""" dtype = lax.dtype(x).type x_2 = lax.square(x) # Log of the term multiplying (1 + sum) log_scale = -dtype(0.5) * x_2 - lax.log(-x) - dtype(0.5 * np.log(2. * np.pi)) return log_scale + lax.log(_log_ndtr_asymptotic_series(x, series_order))
def logsumexp(a, axis=None, b=None, keepdims=False, return_sign=False):
if b is not None:
a, b = jnp.broadcast_arrays(a, b)
dims = _reduction_dims(a, axis)
dimadd = lambda x: lax.expand_dims(x, dims)
amax = lax.reduce(a, _constant_like(a, -np.inf), lax.max, dims)
amax = lax.stop_gradient(
lax.select(lax.is_finite(amax), amax, lax.full_like(amax, 0)))
amax_singletons = dimadd(amax)
if b is None:
out = lax.add(
lax.log(
lax.reduce(lax.exp(lax.sub(a, amax_singletons)),
_constant_like(a, 0), lax.add, dims)), amax)
sign = jnp.where(jnp.isnan(out), np.nan, 1.0).astype(out.dtype)
sign = jnp.where(out == -np.inf, 0.0, sign)
else:
sumexp = lax.reduce(lax.mul(lax.exp(lax.sub(a, amax_singletons)), b),
_constant_like(a, 0), lax.add, dims)
sign = lax.stop_gradient(lax.sign(sumexp))
out = lax.add(lax.log(lax.abs(sumexp)), amax)
if return_sign:
return (dimadd(out), dimadd(sign)) if keepdims else (out, sign)
if b is not None:
out = jnp.where(sign < 0, np.nan, out)
return dimadd(out) if keepdims else out
def logsumexp(a, axis=None, b=None, keepdims=False, return_sign=False):
if b is not None:
a, b = _promote_args_inexact("logsumexp", a, b)
a = jnp.where(b != 0, a, -jnp.inf)
pos_dims, dims = _reduction_dims(a, axis)
amax = jnp.max(a, axis=dims, keepdims=keepdims)
amax = lax.stop_gradient(
lax.select(lax.is_finite(amax), amax, lax.full_like(amax, 0)))
amax_with_dims = amax if keepdims else lax.expand_dims(amax, pos_dims)
if b is None:
out = lax.add(
lax.log(
jnp.sum(lax.exp(lax.sub(a, amax_with_dims)),
axis=dims,
keepdims=keepdims)), amax)
sign = jnp.where(jnp.isnan(out), np.nan, 1.0).astype(out.dtype)
sign = jnp.where(out == -np.inf, 0.0, sign)
else:
sumexp = jnp.sum(lax.mul(lax.exp(lax.sub(a, amax_with_dims)), b),
axis=dims,
keepdims=keepdims)
sign = lax.stop_gradient(lax.sign(sumexp))
out = lax.add(lax.log(lax.abs(sumexp)), amax)
if return_sign:
return (out, sign)
if b is not None:
out = jnp.where(sign < 0, np.nan, out)
return out
def log1m_exp(val):
"""Numerically stable implementation of `log(1 - exp(val))`."""
return lax.cond(
lax.gt(val, lax.log(2.0)),
lambda _: lax.log(-lax.expm1(val)),
lambda _: lax.log1p(-lax.exp(val)),
operand=None,
)
def logpdf(x, a, loc=0, scale=1):
x, a, loc, scale = _promote_args_inexact("gamma.logpdf", x, a, loc, scale)
one = _constant_like(x, 1)
y = lax.div(lax.sub(x, loc), scale)
log_linear_term = lax.sub(lax.mul(lax.sub(a, one), lax.log(y)), y)
shape_terms = lax.add(gammaln(a), lax.log(scale))
log_probs = lax.sub(log_linear_term, shape_terms)
return where(lax.lt(x, loc), -inf, log_probs)
def logpdf(x, b, loc=0, scale=1):
x, b, loc, scale = _promote_args_inexact("pareto.logpdf", x, b, loc, scale)
one = _constant_like(x, 1)
scaled_x = lax.div(lax.sub(x, loc), scale)
normalize_term = lax.log(lax.div(scale, b))
log_probs = lax.neg(
lax.add(normalize_term, lax.mul(lax.add(b, one), lax.log(scaled_x))))
return where(lax.lt(x, lax.add(loc, scale)), -inf, log_probs)
def logpdf(x, a, b, loc=0, scale=1):
x, a, b, loc, scale = _promote_args_inexact("beta.logpdf", x, a, b, loc,
scale)
one = _constant_like(x, 1)
shape_term = lax.neg(betaln(a, b))
y = lax.div(lax.sub(x, loc), scale)
log_linear_term = lax.add(lax.mul(lax.sub(a, one), lax.log(y)),
lax.mul(lax.sub(b, one), lax.log1p(lax.neg(y))))
log_probs = lax.sub(lax.add(shape_term, log_linear_term), lax.log(scale))
return where(logical_or(lax.gt(x, lax.add(loc, scale)), lax.lt(x, loc)),
-inf, log_probs)
def logpdf(x, df, loc=0, scale=1):
x, df, loc, scale = _promote_args_inexact("chi2.logpdf", x, df, loc, scale)
one = _constant_like(x, 1)
two = _constant_like(x, 2)
y = lax.div(lax.sub(x, loc), scale)
df_on_two = lax.div(df, two)
kernel = lax.sub(lax.mul(lax.sub(df_on_two, one), lax.log(y)), lax.div(y,two))
nrml_cnst = lax.neg(lax.add(lax.lgamma(df_on_two),lax.div(lax.mul(lax.log(two), df),two)))
log_probs = lax.add(lax.sub(nrml_cnst, lax.log(scale)), kernel)
return where(lax.lt(x, loc), -inf, log_probs)
def logpmf(k, p, loc=0):
k, p, loc = jnp._promote_args_inexact("geom.logpmf", k, p, loc)
zero = lax._const(k, 0)
one = lax._const(k, 1)
x = lax.sub(k, loc)
log_probs = xlog1py(lax.sub(x, one), -p) + lax.log(p)
return jnp.where(lax.le(x, zero), -jnp.inf, log_probs)
def logpdf(x, loc=0, scale=1):
x, loc, scale = _promote_args_inexact("norm.logpdf", x, loc, scale)
two = _constant_like(x, 2)
scale_sqrd = lax.pow(scale, two)
log_normalizer = lax.log(lax.mul(_constant_like(x, 2 * np.pi), scale_sqrd))
quadratic = lax.div(lax.pow(lax.sub(x, loc), two), scale_sqrd)
return lax.div(lax.neg(lax.add(log_normalizer, quadratic)), two)
def tridiagonal_pos_def_log_det(a, b):
"""Compute the log-determinant of a tridiagonal positive-definite matrix.
Computes the log-determinant for a tridiagonal matrix with main diagonal
`b` (all positive) and lower- / upper- diagonal `a`. Equivalent to
np.linalg.slogdet(diag(a, -1) + diag(b) + diag(a, 1))[1]
Args:
a (array): lower/upper diagonal of matrix, shape `(dim - 1,)`.
b (array): main diagonal of matrix, shape `(dim,)`, all positive.
Returns:
Scalar corresponding to log-determinant.
"""
def log_continuant_recursion(l_i_and_l_i_minus_1, a_i_and_b_i_plus_1):
l_i, l_i_minus_1 = l_i_and_l_i_minus_1
a_i, b_i_plus_1 = a_i_and_b_i_plus_1
l_i_plus_1 = log_diff_exp(
lax.log(b_i_plus_1) + l_i, 2 * lax.log(abs(a_i)) + l_i_minus_1)
return (l_i_plus_1, l_i), None
(l_n, _), _ = lax.scan(log_continuant_recursion, (lax.log(b[0]), 0),
(a, b[1:]))
return l_n
def logaddexp(x1, x2):
x1, x2 = _promote_to_result_dtype(onp.logaddexp, *_promote_shapes(x1, x2))
amax = lax.max(x1, x2)
return lax.add(
amax,
lax.log(lax.add(lax.exp(lax.sub(x1, amax)), lax.exp(lax.sub(x2,
amax)))))
def logpdf(x, loc=0, scale=1):
x, loc, scale = _promote_args_inexact("cauchy.logpdf", x, loc, scale)
pi = _constant_like(x, np.pi)
scaled_x = lax.div(lax.sub(x, loc), scale)
normalize_term = lax.log(lax.mul(pi, scale))
return lax.neg(
lax.add(normalize_term, lax.log1p(lax.mul(scaled_x, scaled_x))))
def _log_taylor(primals_in, series_in):
x, = primals_in
series, = series_in
u = [x] + series
v = [lax.log(x)] + [None] * len(series)
for k in range(1, len(v)):
conv = sum([_scale(k, j) * v[j] * u[k - j] for j in range(1, k)])
v[k] = (u[k] - fact(k - 1) * conv) / u[0]
primal_out, *series_out = v
return primal_out, series_out
def multigammaln(a, d):
d = core.concrete_or_error(int, d, "d argument of multigammaln")
a, d = _promote_args_inexact("multigammaln", a, d)
constant = lax.mul(lax.mul(lax.mul(_constant_like(a, 0.25), d),
lax.sub(d, _constant_like(a, 1))),
lax.log(_constant_like(a, np.pi)))
res = jnp.sum(gammaln(jnp.expand_dims(a, axis=-1) -
lax.div(jnp.arange(d), _constant_like(a, 2))),
axis=-1)
return res + constant
def logsumexp(a, axis=None, b=None, keepdims=False, return_sign=False):
if b is not None:
a, b = _promote_args_inexact("logsumexp", a, b)
a = jnp.where(b != 0, a, -jnp.inf)
else:
a, = _promote_args_inexact("logsumexp", a)
pos_dims, dims = _reduction_dims(a, axis)
amax = jnp.max(a, axis=dims, keepdims=keepdims)
amax = lax.stop_gradient(
lax.select(jnp.isfinite(amax), amax, lax.full_like(amax, 0)))
amax_with_dims = amax if keepdims else lax.expand_dims(amax, pos_dims)
# fast path if the result cannot be negative.
if b is None and not np.issubdtype(a.dtype, np.complexfloating):
out = lax.add(
lax.log(
jnp.sum(lax.exp(lax.sub(a, amax_with_dims)),
axis=dims,
keepdims=keepdims)), amax)
sign = jnp.where(jnp.isnan(out), out, 1.0)
sign = jnp.where(jnp.isneginf(out), 0.0, sign).astype(out.dtype)
else:
expsub = lax.exp(lax.sub(a, amax_with_dims))
if b is not None:
expsub = lax.mul(expsub, b)
sumexp = jnp.sum(expsub, axis=dims, keepdims=keepdims)
sign = lax.stop_gradient(jnp.sign(sumexp))
if np.issubdtype(sumexp.dtype, np.complexfloating):
if return_sign:
sumexp = sign * sumexp
out = lax.add(lax.log(sumexp), amax)
else:
out = lax.add(lax.log(lax.abs(sumexp)), amax)
if return_sign:
return (out, sign)
if b is not None:
if not np.issubdtype(out.dtype, np.complexfloating):
with jax.debug_nans(False):
out = jnp.where(sign < 0, jnp.array(np.nan, dtype=out.dtype),
out)
return out
def _pow_taylor(primals_in, series_in):
u_, r_ = primals_in
x, series = jet(lambda x, y: lax.mul(y, lax.log(x)), primals_in, series_in)
u = [x] + series
v = [u_ ** r_] + [None] * len(series)
for k in range(1, len(v)):
v[k] = fact(k-1) * sum([_scale(k, j) * v[k-j] * u[j] for j in range(1, k+1)])
primal_out, *series_out = v
return primal_out, series_out
def logpdf(x, df, loc=0, scale=1):
x, df, loc, scale = _promote_args_inexact("t.logpdf", x, df, loc, scale)
two = _lax_const(x, 2)
scaled_x = lax.div(lax.sub(x, loc), scale)
df_over_two = lax.div(df, two)
df_plus_one_over_two = lax.add(df_over_two, _lax_const(x, 0.5))
normalize_term_const = lax.mul(lax.mul(scale, scale), _lax_const(x, np.pi))
normalize_term_tmp = lax.div(lax.log(lax.mul(normalize_term_const, df)), two)
normalize_term = lax.sub(lax.add(lax.lgamma(df_over_two), normalize_term_tmp),
lax.lgamma(df_plus_one_over_two))
quadratic = lax.div(lax.mul(scaled_x, scaled_x), df)
return lax.neg(lax.add(normalize_term, lax.mul(df_plus_one_over_two, lax.log1p(quadratic))))
def multigammaln(a, d):
a, = _promote_args_inexact("multigammaln", a)
d = lax.convert_element_type(d, lax.dtype(a))
constant = lax.mul(
lax.mul(lax.mul(_constant_like(a, 0.25), d),
lax.sub(d, _constant_like(a, 1))),
lax.log(_constant_like(a, np.pi)))
res = jnp.sum(gammaln(
jnp.expand_dims(a, axis=-1) -
lax.div(jnp.arange(d), _constant_like(a, 2))),
axis=-1)
return res + constant
def multigammaln(a, d):
d = core.concrete_or_error(int, d, "d argument of multigammaln")
a, d_ = _promote_args_inexact("multigammaln", a, d)
constant = lax.mul(
lax.mul(lax.mul(_lax_const(a, 0.25), d_),
lax.sub(d_, _lax_const(a, 1))), lax.log(_lax_const(a, np.pi)))
b = lax.div(jnp.arange(d, dtype=d_.dtype), _lax_const(a, 2))
res = jnp.sum(gammaln(
jnp.expand_dims(a, axis=-1) -
jnp.expand_dims(b, axis=tuple(range(a.ndim)))),
axis=-1)
return res + constant
def log_I1(orders: int, value, terms=250):
r"""Compute first n log modified bessel function of first kind
.. math ::
\log(I_v(z)) = v*\log(z/2) + \log(\sum_{k=0}^\inf \exp\left[2*k*\log(z/2) - \sum_kk^k log(kk)
- \lgamma(v + k + 1)\right])
:param orders: orders of the log modified bessel function.
:param value: values to compute modified bessel function for
:param terms: truncation of summation
:return: 0 to orders modified bessel function
"""
orders = orders + 1
if value.ndim == 0:
vshape = jnp.shape([1])
else:
vshape = value.shape
value = value.reshape(-1, 1)
flat_vshape = _numel(vshape)
k = jnp.arange(terms)
lgammas_all = lax.lgamma(jnp.arange(1.0, terms + orders + 1))
assert lgammas_all.shape == (orders + terms,
) # lgamma(0) = inf => start from 1
lvalues = lax.log(value / 2) * k.reshape(1, -1)
assert lvalues.shape == (flat_vshape, terms)
lfactorials = lgammas_all[:terms]
assert lfactorials.shape == (terms, )
lgammas = lgammas_all.tile(orders).reshape((orders, -1))
assert lgammas.shape == (orders, terms + orders
) # lgamma(0) = inf => start from 1
indices = k[:orders].reshape(-1, 1) + k.reshape(1, -1)
assert indices.shape == (orders, terms)
seqs = logsumexp(
2 * lvalues[None, :, :] - lfactorials[None, None, :] -
jnp.take_along_axis(lgammas, indices, axis=1)[:, None, :],
-1,
)
assert seqs.shape == (orders, flat_vshape)
i1s = lvalues[..., :orders].T + seqs
assert i1s.shape == (orders, flat_vshape)
return i1s.reshape(-1, *vshape)
def logpdf(x, p):
x, p = _promote_args_inexact("gennorm.logpdf", x, p)
return lax.log(.5 * p) - lax.lgamma(1 / p) - lax.abs(x)**p
def log_ndtr(x, series_order=3):
r"""Log Normal distribution function.
For details of the Normal distribution function see `ndtr`.
This function calculates :math:`\log(\mathrm{ndtr}(x))` by either calling
:math:`\log(\mathrm{ndtr}(x))` or using an asymptotic series. Specifically:
- For `x > upper_segment`, use the approximation `-ndtr(-x)` based on
:math:`\log(1-x) \approx -x, x \ll 1`.
- For `lower_segment < x <= upper_segment`, use the existing `ndtr` technique
and take a log.
- For `x <= lower_segment`, we use the series approximation of `erf` to compute
the log CDF directly.
The `lower_segment` is set based on the precision of the input:
.. math::
\begin{align}
\mathit{lower\_segment} =&
\ \begin{cases}
-20 & x.\mathrm{dtype}=\mathit{float64} \\
-10 & x.\mathrm{dtype}=\mathit{float32} \\
\end{cases} \\
\mathit{upper\_segment} =&
\ \begin{cases}
8& x.\mathrm{dtype}=\mathit{float64} \\
5& x.\mathrm{dtype}=\mathit{float32} \\
\end{cases}
\end{align}
When `x < lower_segment`, the `ndtr` asymptotic series approximation is:
.. math::
\begin{align}
\mathrm{ndtr}(x) =&\ \mathit{scale} * (1 + \mathit{sum}) + R_N \\
\mathit{scale} =&\ \frac{e^{-0.5 x^2}}{-x \sqrt{2 \pi}} \\
\mathit{sum} =&\ \sum_{n=1}^N {-1}^n (2n-1)!! / (x^2)^n \\
R_N =&\ O(e^{-0.5 x^2} (2N+1)!! / |x|^{2N+3})
\end{align}
where :math:`(2n-1)!! = (2n-1) (2n-3) (2n-5) ... (3) (1)` is a
`double-factorial
<https://en.wikipedia.org/wiki/Double_factorial>`_ operator.
Args:
x: an array of type `float32`, `float64`.
series_order: Positive Python integer. Maximum depth to
evaluate the asymptotic expansion. This is the `N` above.
Returns:
an array with `dtype=x.dtype`.
Raises:
TypeError: if `x.dtype` is not handled.
TypeError: if `series_order` is a not Python `integer.`
ValueError: if `series_order` is not in `[0, 30]`.
"""
if not isinstance(series_order, int):
raise TypeError("series_order must be a Python integer.")
if series_order < 0:
raise ValueError("series_order must be non-negative.")
if series_order > 30:
raise ValueError("series_order must be <= 30.")
x = jnp.asarray(x)
dtype = lax.dtype(x)
if dtype == jnp.float64:
lower_segment = _LOGNDTR_FLOAT64_LOWER
upper_segment = _LOGNDTR_FLOAT64_UPPER
elif dtype == jnp.float32:
lower_segment = _LOGNDTR_FLOAT32_LOWER
upper_segment = _LOGNDTR_FLOAT32_UPPER
else:
raise TypeError("x.dtype={} is not supported.".format(np.dtype(dtype)))
# The basic idea here was ported from:
# https://root.cern.ch/doc/v608/SpecFuncCephesInv_8cxx_source.html
# We copy the main idea, with a few changes
# * For x >> 1, and X ~ Normal(0, 1),
# Log[P[X < x]] = Log[1 - P[X < -x]] approx -P[X < -x],
# which extends the range of validity of this function.
# * We use one fixed series_order for all of 'x', rather than adaptive.
# * Our docstring properly reflects that this is an asymptotic series, not a
# Taylor series. We also provided a correct bound on the remainder.
# * We need to use the max/min in the _log_ndtr_lower arg to avoid nan when
# x=0. This happens even though the branch is unchosen because when x=0
# the gradient of a select involves the calculation 1*dy+0*(-inf)=nan
# regardless of whether dy is finite. Note that the minimum is a NOP if
# the branch is chosen.
return jnp.where(
lax.gt(x, upper_segment),
-_ndtr(-x), # log(1-x) ~= -x, x << 1
jnp.where(lax.gt(x, lower_segment),
lax.log(_ndtr(lax.max(x, lower_segment))),
_log_ndtr_lower(lax.min(x, lower_segment), series_order)))
def xlogy(x, y):
x, y = _promote_args_inexact("xlogy", x, y)
x_ok = x != 0.
safe_x = jnp.where(x_ok, x, 1.)
safe_y = jnp.where(x_ok, y, 1.)
return jnp.where(x_ok, lax.mul(safe_x, lax.log(safe_y)), jnp.zeros_like(x))
def xlogy_jvp_lhs(g, x, y, jaxpr, aval, consts):
x, y = _promote_args_like(osp_special.xlogy, x, y)
g, y = _promote_args_like(osp_special.xlogy, g, y)
return lax._safe_mul(lax._brcast(g, y), lax._brcast(lax.log(y), g))
def_deriv(
lax.erf_p, lambda x: lax.mul(lax._const(x, 2. / np.sqrt(np.pi)),
lax.exp(lax.neg(lax.square(x)))))
def def_comp(prim, comp):
"""
Define the jet rule for a primitive in terms of a composition of simpler primitives.
"""
jet_rules[prim] = partial(jet, comp)
def_comp(lax.expm1_p, lambda x: lax.exp(x) - 1)
def_comp(lax.log1p_p, lambda x: lax.log(1 + x))
def_comp(lax.sqrt_p, lambda x: x**0.5)
def_comp(lax.rsqrt_p, lambda x: x**-0.5)
def_comp(lax.asinh_p, lambda x: lax.log(x + lax.sqrt(lax.square(x) + 1)))
def_comp(lax.acosh_p, lambda x: lax.log(x + lax.sqrt(lax.square(x) - 1)))
def_comp(lax.atanh_p, lambda x: 0.5 * lax.log(lax.div(1 + x, 1 - x)))
def_comp(lax.erfc_p, lambda x: 1 - lax.erf(x))
def_comp(lax.rem_p, lambda x, y: x - y * lax.floor(x / y))
def_comp(lax.clamp_p, lambda a, x, b: lax.min(lax.max(a, x), b))
def _erf_inv_rule(primals_in, series_in):
x, = primals_in
series, = series_in
u = [x] + series
def _ndtri(p):
"""Implements ndtri core logic."""
# Constants used in piece-wise rational approximations. Taken from the cephes
# library:
# https://root.cern.ch/doc/v608/SpecFuncCephesInv_8cxx_source.html
p0 = list(
reversed([
-5.99633501014107895267E1, 9.80010754185999661536E1,
-5.66762857469070293439E1, 1.39312609387279679503E1,
-1.23916583867381258016E0
]))
q0 = list(
reversed([
1.0, 1.95448858338141759834E0, 4.67627912898881538453E0,
8.63602421390890590575E1, -2.25462687854119370527E2,
2.00260212380060660359E2, -8.20372256168333339912E1,
1.59056225126211695515E1, -1.18331621121330003142E0
]))
p1 = list(
reversed([
4.05544892305962419923E0, 3.15251094599893866154E1,
5.71628192246421288162E1, 4.40805073893200834700E1,
1.46849561928858024014E1, 2.18663306850790267539E0,
-1.40256079171354495875E-1, -3.50424626827848203418E-2,
-8.57456785154685413611E-4
]))
q1 = list(
reversed([
1.0, 1.57799883256466749731E1, 4.53907635128879210584E1,
4.13172038254672030440E1, 1.50425385692907503408E1,
2.50464946208309415979E0, -1.42182922854787788574E-1,
-3.80806407691578277194E-2, -9.33259480895457427372E-4
]))
p2 = list(
reversed([
3.23774891776946035970E0, 6.91522889068984211695E0,
3.93881025292474443415E0, 1.33303460815807542389E0,
2.01485389549179081538E-1, 1.23716634817820021358E-2,
3.01581553508235416007E-4, 2.65806974686737550832E-6,
6.23974539184983293730E-9
]))
q2 = list(
reversed([
1.0, 6.02427039364742014255E0, 3.67983563856160859403E0,
1.37702099489081330271E0, 2.16236993594496635890E-1,
1.34204006088543189037E-2, 3.28014464682127739104E-4,
2.89247864745380683936E-6, 6.79019408009981274425E-9
]))
dtype = lax.dtype(p).type
shape = jnp.shape(p)
def _create_polynomial(var, coeffs):
"""Compute n_th order polynomial via Horner's method."""
coeffs = np.array(coeffs, dtype)
if not coeffs.size:
return jnp.zeros_like(var)
return coeffs[0] + _create_polynomial(var, coeffs[1:]) * var
maybe_complement_p = jnp.where(p > dtype(-np.expm1(-2.)), dtype(1.) - p, p)
# Write in an arbitrary value in place of 0 for p since 0 will cause NaNs
# later on. The result from the computation when p == 0 is not used so any
# number that doesn't result in NaNs is fine.
sanitized_mcp = jnp.where(maybe_complement_p <= dtype(0.),
jnp.full(shape, dtype(0.5)), maybe_complement_p)
# Compute x for p > exp(-2): x/sqrt(2pi) = w + w**3 P0(w**2)/Q0(w**2).
w = sanitized_mcp - dtype(0.5)
ww = lax.square(w)
x_for_big_p = w + w * ww * (_create_polynomial(ww, p0) /
_create_polynomial(ww, q0))
x_for_big_p *= -dtype(np.sqrt(2. * np.pi))
# Compute x for p <= exp(-2): x = z - log(z)/z - (1/z) P(1/z) / Q(1/z),
# where z = sqrt(-2. * log(p)), and P/Q are chosen between two different
# arrays based on whether p < exp(-32).
z = lax.sqrt(dtype(-2.) * lax.log(sanitized_mcp))
first_term = z - lax.log(z) / z
second_term_small_p = (_create_polynomial(dtype(1.) / z, p2) /
_create_polynomial(dtype(1.) / z, q2) / z)
second_term_otherwise = (_create_polynomial(dtype(1.) / z, p1) /
_create_polynomial(dtype(1.) / z, q1) / z)
x_for_small_p = first_term - second_term_small_p
x_otherwise = first_term - second_term_otherwise
x = jnp.where(sanitized_mcp > dtype(np.exp(-2.)), x_for_big_p,
jnp.where(z >= dtype(8.0), x_for_small_p, x_otherwise))
x = jnp.where(p > dtype(1. - np.exp(-2.)), x, -x)
infinity = jnp.full(shape, dtype(np.inf))
x_nan_replaced = jnp.where(p <= dtype(0.0), -infinity,
jnp.where(p >= dtype(1.0), infinity, x))
return x_nan_replaced
def exp2(x):
x, = _promote_args_inexact("exp2", x)
return lax.exp(lax.mul(lax.log(_constant_like(x, 2)), x))
def logit(x):
x = asarray(x)
return lax.log(lax.div(x, lax.sub(lax._const(x, 1), x)))
def log10(x):
x, = _promote_args_inexact("log10", x)
return lax.div(lax.log(x), lax.log(_constant_like(x, 10)))
