# Value Transforms¶

 coax.value_transforms.ValueTransform Abstract base class for value transforms. coax.value_transforms.LogTransform A simple invertible log-transform.

This module contains some useful value transforms. These are functions that can be used to rescale or warp the returns for more a more robust training signal, see e.g. coax.value_transforms.LogTransform.

## Object Reference¶

class coax.value_transforms.ValueTransform(transform_func, inverse_func)[source]

Abstract base class for value transforms. See coax.value_transforms.LogTransform for a specific implementation.

property inverse_func

The inverse transformation function $$y\mapsto x=f^{-1}(y)$$.

Parameters:

y (ndarray) – The values in their transformed representation.

Returns:

x (ndarray) – The values in their original representation.

property transform_func

The transformation function $$x\mapsto y=f(x)$$.

Parameters:

x (ndarray) – The values in their original representation.

Returns:

y (ndarray) – The values in their transformed representation.

class coax.value_transforms.LogTransform(scale=1.0)[source]

A simple invertible log-transform.

$x\ \mapsto\ y\ =\ \lambda\,\text{sign}(x)\, \log\left(1+\frac{|x|}{\lambda}\right)$

with inverse:

$y\ \mapsto\ x\ =\ \lambda\,\text{sign}(y)\, \left(\text{e}^{|y|/\lambda} - 1\right)$

This transform logarithmically supresses large values $$|x|\gg1$$ and smoothly interpolates to the identity transform for small values $$|x|\sim1$$ (see figure below).

Parameters:

scale (positive float, optional) – The scale $$\lambda>0$$ of the linear-to-log cross-over. Smaller values for $$\lambda$$ translate into earlier onset of the cross-over.

property inverse_func

The inverse transformation function $$y\mapsto x=f^{-1}(y)$$.

Parameters:

y (ndarray) – The values in their transformed representation.

Returns:

x (ndarray) – The values in their original representation.

property transform_func

The transformation function $$x\mapsto y=f(x)$$.

Parameters:

x (ndarray) – The values in their original representation.

Returns:

y (ndarray) – The values in their transformed representation.