Incompatibility with autograd package.

[ThomasAuzinger]

I am using the colormath package together with the autograd package – a combination, which does not work. So far, I identified two problems that seem to be easily fixable:

1. Float conversions are not supported by autograd:
   The colormath package uses float casts, e.g., self.spec_340nm = float(spec_340nm) (link); however, these fail when autograd uses the ArrayNode data type instead of conventional numbers.

2. The builtin math package is not supported by autograd:
   The colormath package uses explicit function calls to math.pow, e.g., nonlinear_channels[channel] = 1.055 * math.pow(v, 1 / 2.4) - 0.055 link; however, the math package is not supported by autograd.

I am aware that it is not the job of the maintainers of colormath to keep it compatible with every other package; in this case, however, I think the required changes are trivial and should not cause problems. Thus, I wanted to know, if there are any reason not to do the following:

1. Remove explicit float conversions in colormath.

2. Replace the math.pow function with the corresponding operator **, which is more portable.

If these changes are acceptable, I would prepare a corresponding merge request.

Cheers,
Thomas

[gtaylor]

Hello @ThomasAuzinger,

We'd need to go to Python futures division for Python 2.x, which would be a pretty major undertaking at this point. I'm not super motivated to do all of the verification work to ensure such a big change doesn't break our math. With that said, I'm happy to change my tune if enough people request this.

I would accept a math.pow -> ** PR, though.

I admit to being confused as to how autograd just doesn't flat out support Python primitives like these, though. That sounds all kinds of weird to me.

[ThomasAuzinger]

Hi @gtaylor ,

Thanks for your fast answer. I will prepare the ** pull request.

I admit to being confused as to how autograd just doesn't flat out support Python primitives like these, though. That sounds all kinds of weird to me.

I am not completely sure what you mean with 'flat out support Python primitives' (i.e., is 'flat out' the verb or 'support'?). Anyhow, I wrote an issue for autograd in this respect that can be found here.
In summary, I think that the issue is that a __float__(self) overload must return a float type. However, autograd is using its own data type ArrayNode that tracks all function application to its values to compute the gradient. These two requirements seem incompatible.

[gtaylor]

Going to go on ahead to close this as not actionable.