numpy.arccos(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'arccos'>
Trigonometric inverse cosine, elementwise.
The inverse of cos
so that, if y = cos(x)
, then x = arccos(y)
.
Parameters: 


Returns: 

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 yields nan
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.
M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 79. http://www.math.sfu.ca/~cbm/aands/
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()
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https://docs.scipy.org/doc/numpy1.17.0/reference/generated/numpy.arccos.html