scipy.special.expn#
- scipy.special.expn(n, x, out=None) = <ufunc 'expn'>#
Generalized exponential integral En.
For integer \(n \geq 0\) and real \(x \geq 0\) the generalized exponential integral is defined as [dlmf]
\[E_n(x) = x^{n - 1} \int_x^\infty \frac{e^{-t}}{t^n} dt.\]- Parameters:
- narray_like
Non-negative integers
- xarray_like
Real argument
- outndarray, optional
Optional output array for the function results
- Returns:
- scalar or ndarray
Values of the generalized exponential integral
Notes
expn
has experimental support for Python Array API Standard compatible backends in addition to NumPy. Please consider testing these features by setting an environment variableSCIPY_ARRAY_API=1
and providing CuPy, PyTorch, JAX, or Dask arrays as array arguments. The following combinations of backend and device (or other capability) are supported.Library
CPU
GPU
NumPy
✅
n/a
CuPy
n/a
✅
PyTorch
✅
⛔
JAX
✅
✅
Dask
✅
n/a
See Support for the array API standard for more information.
References
[dlmf]Digital Library of Mathematical Functions, 8.19.2 https://dlmf.nist.gov/8.19#E2
Examples
>>> import numpy as np >>> import scipy.special as sc
Its domain is nonnegative n and x.
>>> sc.expn(-1, 1.0), sc.expn(1, -1.0) (nan, nan)
It has a pole at
x = 0
forn = 1, 2
; for largern
it is equal to1 / (n - 1)
.>>> sc.expn([0, 1, 2, 3, 4], 0) array([ inf, inf, 1. , 0.5 , 0.33333333])
For n equal to 0 it reduces to
exp(-x) / x
.>>> x = np.array([1, 2, 3, 4]) >>> sc.expn(0, x) array([0.36787944, 0.06766764, 0.01659569, 0.00457891]) >>> np.exp(-x) / x array([0.36787944, 0.06766764, 0.01659569, 0.00457891])
For n equal to 1 it reduces to
exp1
.>>> sc.expn(1, x) array([0.21938393, 0.04890051, 0.01304838, 0.00377935]) >>> sc.exp1(x) array([0.21938393, 0.04890051, 0.01304838, 0.00377935])