-
numpy.arccos(x[, out]) =
-
Trigonometric inverse cosine, element-wise.
The inverse of
cos
so that, ify = cos(x)
, thenx = arccos(y)
.Parameters: x : array_like
x
-coordinate on the unit circle. For real arguments, the domain is [-1, 1].out : ndarray, optional
Array of the same shape as
a
, to store results in. Seedoc.ufuncs
(Section ?Output arguments?) for more details.Returns: angle : ndarray
The angle of the ray intersecting the unit circle at the given
x
-coordinate in radians [0, pi]. Ifx
is a scalar then a scalar is returned, otherwise an array of the same shape asx
is returned.Notes
arccos
is a multivalued function: for eachx
there are infinitely many numbersz
such thatcos(z) = x
. The convention is to return the anglez
whose real part lies in[0, pi]
.For real-valued input data types,
arccos
always returns real output. For each value that cannot be expressed as a real number or infinity, it yieldsnan
and sets theinvalid
floating point error flag.For complex-valued input,
arccos
is a complex analytic function that has branch cuts[-inf, -1]
and[1, inf]
and is continuous from above on the former and from below on the latter.The inverse
cos
is also known asacos
or cos^-1.References
M. Abramowitz and I.A. Stegun, ?Handbook of Mathematical Functions?, 10th printing, 1964, pp. 79. http://www.math.sfu.ca/~cbm/aands/
Examples
We expect the arccos of 1 to be 0, and of -1 to be pi:
>>> np.arccos([1, -1]) array([ 0. , 3.14159265])
Plot arccos:
>>> import matplotlib.pyplot as plt >>> x = np.linspace(-1, 1, num=100) >>> plt.plot(x, np.arccos(x)) >>> plt.axis('tight') >>> plt.show()
(Source code, png, pdf)
numpy.arccos()
2017-01-10 18:12:40
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