log1p(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj])

Some inconsistencies with the Dask version may exist.

Return the natural logarithm of one plus the input array, element-wise.

Calculates log(1 + x) .

Notes

For real-valued input, log1p is accurate also for x so small that :None:None:`1 + x == 1` in floating-point accuracy.

Logarithm is a multivalued function: for each x there is an infinite number of :None:None:`z` such that :None:None:`exp(z) = 1 + x`. The convention is to return the :None:None:`z` whose imaginary part lies in :None:None:`[-pi, pi]`.

For real-valued input data types, log1p always returns real output. For each value that cannot be expressed as a real number or infinity, it yields nan and sets the :None:None:`invalid` floating point error flag.

For complex-valued input, log1p is a complex analytical function that has a branch cut :None:None:`[-inf, -1]` and is continuous from above on it. log1p handles the floating-point negative zero as an infinitesimal negative number, conforming to the C99 standard.

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 :None:None:`out` array will be set to the ufunc result. Elsewhere, the :None:None:`out` array will retain its original value. Note that if an uninitialized :None:None:`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 <ufuncs.kwargs> .

Returns

y : ndarray

Natural logarithm of :None:None:`1 + x`, element-wise. This is a scalar if x is a scalar.

This docstring was copied from numpy.log1p.

See Also

expm1

exp(x) - 1 , the inverse of :None:None:`log1p`.

Examples

This example is valid syntax, but we were not able to check execution

>>> np.log1p(1e-99)  # doctest: +SKIP
1e-99

This example is valid syntax, but we were not able to check execution

>>> np.log(1 + 1e-99)  # doctest: +SKIP
0.0

See :

Back References

The following pages refer to to this document either explicitly or contain code examples using this.

dask.array.ufunc.expm1 dask.array.ufunc.log2 dask.array.ufunc.log1p dask.array.ufunc.log

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