flopscope.

flopscope.numpy.logaddexp2

fnp.logaddexp2(*args, **kwargs)[flopscope source][numpy source]

Logarithm of the sum of exponentiations of the inputs in base-2.

Adapted from NumPy docs np.logaddexp2

Areacore
Typecounted
NumPy Refnp.logaddexp2
Cost
16×numel(output)\text{numel}(\text{output})
Flopscope Context

log2(2**x1 + 2**x2) element-wise.

Calculates log2(2**x1 + 2**x2). This function is useful in machine learning when the calculated probabilities of events may be so small as to exceed the range of normal floating point numbers. In such cases the base-2 logarithm of the calculated probability can be used instead. This function allows adding probabilities stored in such a fashion.

Parameters

x1, x2:array_like

Input values. If x1.shape != x2.shape, they must be broadcastable to a common shape (which becomes the shape of the output).

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

result:ndarray

Base-2 logarithm of 2**x1 + 2**x2. This is a scalar if both x1 and x2 are scalars.

See also

Examples

>>> import flopscope.numpy as fnp
>>> prob1 = flops.log2(1e-50)
>>> prob2 = flops.log2(2.5e-50)
>>> prob12 = flops.logaddexp2(prob1, prob2)
>>> prob1, prob2, prob12
(-166.09640474436813, -164.77447664948076, -164.28904982231052)
>>> 2**prob12
3.4999999999999914e-50