numpy.exp()

numpy.exp(x[, out]) =

Calculate the exponential of all elements in the input array.

Parameters:

Parameters:	x : array_like Input values.
Returns:	out : ndarray Output array, element-wise exponential of `x`.

x : array_like

Input values.

Returns:

out : ndarray

Output array, element-wise exponential of x.

Notes

The irrational number e is also known as Euler?s number. It is approximately 2.718281, and is the base of the natural logarithm, ln (this means that, if $x = \ln y = \log_e y$ , then $e^x = y$ . For real input, exp(x) is always positive.

For complex arguments, x = a + ib, we can write $e^x = e^a e^{ib}$ . The first term, $e^a$ , is already known (it is the real argument, described above). The second term, $e^{ib}$ , is $\cos b + i \sin b$ , a function with magnitude 1 and a periodic phase.

References

[R18]

Wikipedia, ?Exponential function?, http://en.wikipedia.org/wiki/Exponential_function

[R19]

M. Abramovitz and I. A. Stegun, ?Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables,? Dover, 1964, p. 69, http://www.math.sfu.ca/~cbm/aands/page_69.htm

Examples

Plot the magnitude and phase of exp(x) in the complex plane:

>>> import matplotlib.pyplot as plt

>>> x = np.linspace(-2*np.pi, 2*np.pi, 100)
>>> xx = x + 1j * x[:, np.newaxis] # a + ib over complex plane
>>> out = np.exp(xx)

>>> plt.subplot(121)
>>> plt.imshow(np.abs(out),
...            extent=[-2*np.pi, 2*np.pi, -2*np.pi, 2*np.pi])
>>> plt.title('Magnitude of exp(x)')

>>> plt.subplot(122)
>>> plt.imshow(np.angle(out),
...            extent=[-2*np.pi, 2*np.pi, -2*np.pi, 2*np.pi])
>>> plt.title('Phase (angle) of exp(x)')
>>> plt.show()

(Source code, png, pdf)

Links:

https://docs.scipy.org/doc/numpy-1.11.0/reference/generated/numpy.exp.html

doc_NumPy

2025-01-10 15:47:30

Comments