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# scipy.special.cosm1

scipy.special.cosm1(x, out=None) = <ufunc 'cosm1'>

  cos(x) - 1 for use when x is near zero.

  Parameters:
    x array_like

      Real valued argument.

    out ndarray, optional

      Optional output array for the function results.

  Returns:
    scalar or ndarray

      Values of `cos(x) - 1`.

  See also

  `expm1`, `log1p`

  Notes

  Array API Standard Support

  `cosm1` has experimental support for Python Array API Standard compatible backends in addition to NumPy. Please consider testing these features by setting an environment variable `SCIPY_ARRAY_API=1` and providing CuPy, PyTorch, JAX, or Dask arrays as array arguments. The following combinations of backend and device (or other capability) are supported.

  Library | CPU | GPU
  --- | --- | ---
  NumPy | ✅ | n/a
  CuPy | n/a | ✅
  PyTorch | ✅ | ⛔
  JAX | ⚠️ no JIT | ⛔
  Dask | ✅ | n/a

  > See Support for the array API standard for more information.

  Examples

      >>> import numpy as np
      >>> import scipy.special as sc

  It is more accurate than computing `cos(x) - 1` directly for `x` around 0.

      >>> x = 1e-30
      >>> np.cos(x) - 1
      0.0
      >>> sc.cosm1(x)
      -5.0000000000000005e-61