mygrad.logaddexp2#

class mygrad.logaddexp2(x1: ArrayLike, x2: ArrayLike, out: Tensor | ndarray | None = None, *, where: Mask = True, dtype: DTypeLikeReals = None, constant: bool | None = None)#

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

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.

This docstring was adapted from that of numpy.logaddexp2 [1]

Parameters:
x1, x2ArrayLike

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

outOptional[Union[Tensor, ndarray]]

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 tensor is returned.

constantOptional[bool]

If True, this tensor is treated as a constant, and thus does not facilitate back propagation (i.e. constant.grad will always return None).

Defaults to False for float-type data. Defaults to True for integer-type data.

Integer-type tensors must be constant.

whereMask

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

dtypeOptional[DTypeLikeReals]

The dtype of the resulting tensor.

Returns:
logaddexp2Tensor

Base-2 logarithm of 2**x1 + 2**x2.

See also

logaddexp

Logarithm of the sum of exponentiations of the inputs.

References

Examples

>>> import mygrad as mg
>>> prob1 = mg.log2(1e-50)
>>> prob2 = mg.log2(2.5e-50)
>>> prob12 = mg.logaddexp2(prob1, prob2)
>>> prob1, prob2, prob12
(Tensor(-166.09640474436813), Tensor(-164.77447664948076), Tensor(-164.28904982231052))
>>> 2 ** prob12
Tensor(3.4999999999999914e-50)
Attributes:
signature

Methods

accumulate([axis, dtype, out, constant])

Not implemented

at(indices[, b, constant])

Not implemented

outer(b, *[, dtype, out])

Not Implemented

reduce([axis, dtype, out, keepdims, ...])

Not Implemented

reduceat(indices[, axis, dtype, out])

Not Implemented

resolve_dtypes(dtypes, *[, signature, ...])

Find the dtypes NumPy will use for the operation.
__init__(*args, **kwargs)#

Methods

__init__(*args, **kwargs)

accumulate([axis, dtype, out, constant])

Not implemented

at(indices[, b, constant])

Not implemented

outer(b, *[, dtype, out])

Not Implemented

reduce([axis, dtype, out, keepdims, ...])

Not Implemented

reduceat(indices[, axis, dtype, out])

Not Implemented

resolve_dtypes(dtypes, *[, signature, ...])

Find the dtypes NumPy will use for the operation.

Attributes

identity

nargs

nin

nout

ntypes

signature

types