scipy.special.ndtri_exp

scipy.special.ndtri_exp(y) = <ufunc 'ndtri_exp'>

Inverse of log_ndtr vs x. Allows for greater precision than ndtri composed with numpy.exp for very small values of y and for y close to 0.

Parameters

yarray_like of float

Returns

scalar or ndarray

Inverse of the log CDF of the standard normal distribution, evaluated at y.

See also

log_ndtr, ndtri, ndtr

Examples

>>> import scipy.special as sc

ndtri_exp agrees with the naive implementation when the latter does not suffer from underflow.

>>> sc.ndtri_exp(-1)
-0.33747496376420244
>>> sc.ndtri(np.exp(-1))
-0.33747496376420244

For extreme values of y, the naive approach fails

>>> sc.ndtri(np.exp(-800))
-inf
>>> sc.ndtri(np.exp(-1e-20))
inf

whereas ndtri_exp is still able to compute the result to high precision.

>>> sc.ndtri_exp(-800)
-39.88469483825668
>>> sc.ndtri_exp(-1e-20)
9.262340089798409

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