pytorch-image-models/timm/layers/activations_me.py

""" Activations (memory-efficient w/ custom autograd)

A collection of activations fn and modules with a common interface so that they can
easily be swapped. All have an `inplace` arg even if not used.

These activations are not compatible with jit scripting or ONNX export of the model, please use
basic versions of the activations.

Hacked together by / Copyright 2020 Ross Wightman
"""

import torch
from torch import nn as nn
from torch.nn import functional as F


def swish_fwd(x):
    return x.mul(torch.sigmoid(x))


def swish_bwd(x, grad_output):
    x_sigmoid = torch.sigmoid(x)
    return grad_output * (x_sigmoid * (1 + x * (1 - x_sigmoid)))


class SwishAutoFn(torch.autograd.Function):
    """ optimised Swish w/ memory-efficient checkpoint
    Inspired by conversation btw Jeremy Howard & Adam Pazske
    https://twitter.com/jeremyphoward/status/1188251041835315200
    """
    @staticmethod
    def symbolic(g, x):
        return g.op("Mul", x, g.op("Sigmoid", x))

    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return swish_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_tensors[0]
        return swish_bwd(x, grad_output)


def swish_me(x, inplace=False):
    return SwishAutoFn.apply(x)


class SwishMe(nn.Module):
    def __init__(self, inplace: bool = False):
        super(SwishMe, self).__init__()

    def forward(self, x):
        return SwishAutoFn.apply(x)


def mish_fwd(x):
    return x.mul(torch.tanh(F.softplus(x)))


def mish_bwd(x, grad_output):
    x_sigmoid = torch.sigmoid(x)
    x_tanh_sp = F.softplus(x).tanh()
    return grad_output.mul(x_tanh_sp + x * x_sigmoid * (1 - x_tanh_sp * x_tanh_sp))


class MishAutoFn(torch.autograd.Function):
    """ Mish: A Self Regularized Non-Monotonic Neural Activation Function - https://arxiv.org/abs/1908.08681
    A memory efficient variant of Mish
    """
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return mish_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_tensors[0]
        return mish_bwd(x, grad_output)


def mish_me(x, inplace=False):
    return MishAutoFn.apply(x)


class MishMe(nn.Module):
    def __init__(self, inplace: bool = False):
        super(MishMe, self).__init__()

    def forward(self, x):
        return MishAutoFn.apply(x)


def hard_sigmoid_fwd(x, inplace: bool = False):
    return (x + 3).clamp(min=0, max=6).div(6.)


def hard_sigmoid_bwd(x, grad_output):
    m = torch.ones_like(x) * ((x >= -3.) & (x <= 3.)) / 6.
    return grad_output * m


class HardSigmoidAutoFn(torch.autograd.Function):
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return hard_sigmoid_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_tensors[0]
        return hard_sigmoid_bwd(x, grad_output)


def hard_sigmoid_me(x, inplace: bool = False):
    return HardSigmoidAutoFn.apply(x)


class HardSigmoidMe(nn.Module):
    def __init__(self, inplace: bool = False):
        super(HardSigmoidMe, self).__init__()

    def forward(self, x):
        return HardSigmoidAutoFn.apply(x)


def hard_swish_fwd(x):
    return x * (x + 3).clamp(min=0, max=6).div(6.)


def hard_swish_bwd(x, grad_output):
    m = torch.ones_like(x) * (x >= 3.)
    m = torch.where((x >= -3.) & (x <= 3.),  x / 3. + .5, m)
    return grad_output * m


class HardSwishAutoFn(torch.autograd.Function):
    """A memory efficient HardSwish activation"""
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return hard_swish_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_tensors[0]
        return hard_swish_bwd(x, grad_output)

    @staticmethod
    def symbolic(g, self):
        input = g.op("Add", self, g.op('Constant', value_t=torch.tensor(3, dtype=torch.float)))
        hardtanh_ = g.op("Clip", input, g.op('Constant', value_t=torch.tensor(0, dtype=torch.float)), g.op('Constant', value_t=torch.tensor(6, dtype=torch.float)))
        hardtanh_ = g.op("Div", hardtanh_, g.op('Constant', value_t=torch.tensor(6, dtype=torch.float)))
        return g.op("Mul", self, hardtanh_)


def hard_swish_me(x, inplace=False):
    return HardSwishAutoFn.apply(x)


class HardSwishMe(nn.Module):
    def __init__(self, inplace: bool = False):
        super(HardSwishMe, self).__init__()

    def forward(self, x):
        return HardSwishAutoFn.apply(x)


def hard_mish_fwd(x):
    return 0.5 * x * (x + 2).clamp(min=0, max=2)


def hard_mish_bwd(x, grad_output):
    m = torch.ones_like(x) * (x >= -2.)
    m = torch.where((x >= -2.) & (x <= 0.), x + 1., m)
    return grad_output * m


class HardMishAutoFn(torch.autograd.Function):
    """ A memory efficient variant of Hard Mish
    Experimental, based on notes by Mish author Diganta Misra at
      https://github.com/digantamisra98/H-Mish/blob/0da20d4bc58e696b6803f2523c58d3c8a82782d0/README.md
    """
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return hard_mish_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_tensors[0]
        return hard_mish_bwd(x, grad_output)


def hard_mish_me(x, inplace: bool = False):
    return HardMishAutoFn.apply(x)


class HardMishMe(nn.Module):
    def __init__(self, inplace: bool = False):
        super(HardMishMe, self).__init__()

    def forward(self, x):
        return HardMishAutoFn.apply(x)