# xarray.ufuncs.expm1¶

xarray.ufuncs.expm1(*args, **kwargs) = <xarray.ufuncs._UFuncDispatcher object>

xarray specific variant of numpy.expm1. Handles xarray.Dataset, xarray.DataArray, xarray.Variable, numpy.ndarray and dask.array.Array objects with automatic dispatching.

Documentation from numpy:

expm1(x, /, out=None, *, where=True, casting=’same_kind’, order=’K’, dtype=None, subok=True[, signature, extobj])

Calculate exp(x) - 1 for all elements in the array.

Parameters
• x (array_like) – Input values.

• 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) – This condition is broadcast over the input. At locations where the condition is True, the out array will be set to the ufunc result. Elsewhere, the out array will retain its original value. Note that if an uninitialized out array is created via the default out=None, locations within it where the condition is False will remain uninitialized.

• **kwargs – For other keyword-only arguments, see the ufunc docs.

Returns

out – Element-wise exponential minus one: out = exp(x) - 1. This is a scalar if x is a scalar.

Return type

ndarray or scalar

log1p

log(1 + x), the inverse of expm1.

Notes

This function provides greater precision than exp(x) - 1 for small values of x.

Examples

The true value of exp(1e-10) - 1 is 1.00000000005e-10 to about 32 significant digits. This example shows the superiority of expm1 in this case.

>>> np.expm1(1e-10)
1.00000000005e-10
>>> np.exp(1e-10) - 1
1.000000082740371e-10