numpy.
i0
Modified Bessel function of the first kind, order 0.
Usually denoted
System Message: WARNING/2 (I_0)
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Argument of the Bessel function.
The modified Bessel function evaluated at each of the elements of x.
If argument consists exclusively of int dtypes.
See also
scipy.special.i0, scipy.special.iv, scipy.special.ive
scipy.special.i0
scipy.special.iv
scipy.special.ive
Notes
The scipy implementation is recommended over this function: it is a proper ufunc written in C, and more than an order of magnitude faster.
We use the algorithm published by Clenshaw [1] and referenced by Abramowitz and Stegun [2], for which the function domain is partitioned into the two intervals [0,8] and (8,inf), and Chebyshev polynomial expansions are employed in each interval. Relative error on the domain [0,30] using IEEE arithmetic is documented [3] as having a peak of 5.8e-16 with an rms of 1.4e-16 (n = 30000).
References
C. W. Clenshaw, “Chebyshev series for mathematical functions”, in National Physical Laboratory Mathematical Tables, vol. 5, London: Her Majesty’s Stationery Office, 1962.
M. Abramowitz and I. A. Stegun, Handbook of Mathematical Functions, 10th printing, New York: Dover, 1964, pp. 379. http://www.math.sfu.ca/~cbm/aands/page_379.htm
http://kobesearch.cpan.org/htdocs/Math-Cephes/Math/Cephes.html
Examples
>>> np.i0(0.) array(1.0) # may vary >>> np.i0([0., 1. + 2j]) array([ 1.00000000+0.j , 0.18785373+0.64616944j]) # may vary