numpy.exp

numpy.exp(x[, out]) = <ufunc 'exp'>

Calculate the exponential of all elements in the input array.

Parameters :

x : array_like

Input values.

Returns :

out : ndarray

Output array, element-wise exponential of x.

See also

expm1

Calculate exp(x) - 1 for all elements in the array.

exp2

Calculate 2**x for all elements in the array.

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

System Message: WARNING/2 (x = \ln y = \log_e y)

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, then

System Message: WARNING/2 (e^x = y)

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. For real input, exp(x) is always positive.

For complex arguments, x = a + ib, we can write

System Message: WARNING/2 (e^x = e^a e^{ib})

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. The first term,

System Message: WARNING/2 (e^a)

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, is already known (it is the real argument, described above). The second term,

System Message: WARNING/2 (e^{ib})

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, is

System Message: WARNING/2 (\cos b + i \sin b)

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, 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)