# xarray.ufuncs.arccos

`xarray.ufuncs.``arccos` = <xarray.ufuncs._UFuncDispatcher object>

  xarray specific variant of numpy.arccos. Handles xarray.Dataset, xarray.DataArray, xarray.Variable, numpy.ndarray and dask.array.Array objects with automatic dispatching.

  Documentation from numpy:

  arccos(x, /, out=None, *, where=True, casting=’same_kind’, order=’K’, dtype=None, subok=True[, signature, extobj])

  Trigonometric inverse cosine, element-wise.

  The inverse of cos so that, if `y = cos(x)`, then `x = arccos(y)`.

  Parameters:

  x : array_like

  > x-coordinate on the unit circle. For real arguments, the domain is [-1, 1].

  out : ndarray, None, or tuple of ndarray and None, optional

  > A location into which the result is stored. If provided, it must have a shape that the inputs broadcast to. If not provided or None, a freshly-allocated array is returned. A tuple (possible only as a keyword argument) must have length equal to the number of outputs.

  where : array_like, optional

  > Values of True indicate to calculate the ufunc at that position, values of False indicate to leave the value in the output alone.

  **kwargs

  > For other keyword-only arguments, see the ufunc docs.

  Returns:

  angle : ndarray

  > The angle of the ray intersecting the unit circle at the given x-coordinate 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.

  See also

  `cos`, `arctan`, `arcsin`, `emath.arccos`

  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 real-valued 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 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 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()