numpy.arccos¶

numpy.
arccos
(x[, out]) = <ufunc 'arccos'>¶ Trigonometric inverse cosine, elementwise.
The inverse of
cos
so that, ify = cos(x)
, thenx = arccos(y)
.Parameters: x : array_like
xcoordinate 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. See
doc.ufuncs
(Section “Output arguments”) for more details.Returns: angle : ndarray
The angle of the ray intersecting the unit circle at the given xcoordinate in radians [0, pi]. If x is a scalar then a scalar is returned, otherwise an array of the same shape as x is returned.
Notes
arccos
is a multivalued function: for each x there are infinitely many numbers z such that cos(z) = x. The convention is to return the angle z whose real part lies in [0, pi].For realvalued 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 the invalid floating point error flag.For complexvalued 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 as acos 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)