/examples/pytorch/pointcloud/bipointnet/basic.py

import torch
import torch.nn.functional as F
import torch.nn as nn
from torch.nn.modules.utils import _single
from torch.autograd import Function
from torch.nn import Parameter
import dgl


class BinaryQuantize(Function):
    @staticmethod
    def forward(ctx, input):
        ctx.save_for_backward(input)
        out = torch.sign(input)
        return out

    @staticmethod
    def backward(ctx, grad_output):
        input = ctx.saved_tensors
        grad_input = grad_output
        grad_input[input[0].gt(1)] = 0
        grad_input[input[0].lt(-1)] = 0
        return grad_input


class BiLinearLSR(torch.nn.Linear):
    def __init__(self, in_features, out_features, bias=False, binary_act=True):
        super(BiLinearLSR, self).__init__(in_features, out_features, bias=bias)
        self.binary_act = binary_act

        # must register a nn.Parameter placeholder for model loading
        # self.register_parameter('scale', None) doesn't register None into state_dict
        # so it leads to unexpected key error when loading saved model
        # hence, init scale with Parameter
        # however, Parameter(None) actually has size [0], not [] as a scalar
        # hence, init it using the following trick
        self.register_parameter('scale', Parameter(torch.Tensor([0.0]).squeeze()))

    def reset_scale(self, input):
        bw = self.weight
        ba = input
        bw = bw - bw.mean()
        self.scale = Parameter((F.linear(ba, bw).std() / F.linear(torch.sign(ba), torch.sign(bw)).std()).float().to(ba.device))
        # corner case when ba is all 0.0
        if torch.isnan(self.scale):
            self.scale = Parameter((bw.std() / torch.sign(bw).std()).float().to(ba.device))

    def forward(self, input):
        bw = self.weight
        ba = input
        bw = bw - bw.mean()

        if self.scale.item() == 0.0:
            self.reset_scale(input)

        bw = BinaryQuantize().apply(bw)
        bw = bw * self.scale
        if self.binary_act:
            ba = BinaryQuantize().apply(ba)
        output = F.linear(ba, bw)
        return output


class BiLinear(torch.nn.Linear):
    def __init__(self, in_features, out_features, bias=True, binary_act=True):
        super(BiLinear, self).__init__(in_features, out_features, bias=True)
        self.binary_act = binary_act
        self.output_ = None

    def forward(self, input):
        bw = self.weight
        ba = input
        bw = BinaryQuantize().apply(bw)
        if self.binary_act:
            ba = BinaryQuantize().apply(ba)
        output = F.linear(ba, bw, self.bias)
        self.output_ = output
        return output


class BiConv2d(torch.nn.Conv2d):
    def __init__(self, in_channels, out_channels, kernel_size, stride=1,
                 padding=0, dilation=1, groups=1,
                 bias=True, padding_mode='zeros'):
        super(BiConv2d, self).__init__(
            in_channels, out_channels, kernel_size, stride, padding, dilation,
            groups, bias, padding_mode)

    def forward(self, input):

        bw = self.weight
        ba = input
        bw = bw - bw.mean()
        bw = BinaryQuantize().apply(bw)
        ba = BinaryQuantize().apply(ba)

        if self.padding_mode == 'circular':
            expanded_padding = ((self.padding[0] + 1) // 2, self.padding[0] // 2)
            return F.conv2d(F.pad(ba, expanded_padding, mode='circular'),
                            bw, self.bias, self.stride,
                            _single(0), self.dilation, self.groups)    
        return F.conv2d(ba, bw, self.bias, self.stride,
                        self.padding, self.dilation, self.groups)


def square_distance(src, dst):
    '''
    Adapted from https://github.com/yanx27/Pointnet_Pointnet2_pytorch
    '''
    B, N, _ = src.shape
    _, M, _ = dst.shape
    dist = -2 * torch.matmul(src, dst.permute(0, 2, 1))
    dist += torch.sum(src ** 2, -1).view(B, N, 1)
    dist += torch.sum(dst ** 2, -1).view(B, 1, M)
    return dist

def index_points(points, idx):
    '''
    Adapted from https://github.com/yanx27/Pointnet_Pointnet2_pytorch
    '''
    device = points.device
    B = points.shape[0]
    view_shape = list(idx.shape)
    view_shape[1:] = [1] * (len(view_shape) - 1)
    repeat_shape = list(idx.shape)
    repeat_shape[0] = 1
    batch_indices = torch.arange(B, dtype=torch.long).to(device).view(view_shape).repeat(repeat_shape)
    new_points = points[batch_indices, idx, :]
    return new_points


class FixedRadiusNearNeighbors(nn.Module):
    '''
    Ball Query - Find the neighbors with-in a fixed radius
    '''
    def __init__(self, radius, n_neighbor):
        super(FixedRadiusNearNeighbors, self).__init__()
        self.radius = radius
        self.n_neighbor = n_neighbor

    def forward(self, pos, centroids):
        '''
        Adapted from https://github.com/yanx27/Pointnet_Pointnet2_pytorch
        '''
        device = pos.device
        B, N, _ = pos.shape
        center_pos = index_points(pos, centroids)
        _, S, _ = center_pos.shape
        group_idx = torch.arange(N, dtype=torch.long).to(device).view(1, 1, N).repeat([B, S, 1])
        sqrdists = square_distance(center_pos, pos)
        group_idx[sqrdists > self.radius ** 2] = N
        group_idx = group_idx.sort(dim=-1)[0][:, :, :self.n_neighbor]
        group_first = group_idx[:, :, 0].view(B, S, 1).repeat([1, 1, self.n_neighbor])
        mask = group_idx == N
        group_idx[mask] = group_first[mask]
        return group_idx


class FixedRadiusNNGraph(nn.Module):
    '''
    Build NN graph
    '''
    def __init__(self, radius, n_neighbor):
        super(FixedRadiusNNGraph, self).__init__()
        self.radius = radius
        self.n_neighbor = n_neighbor
        self.frnn = FixedRadiusNearNeighbors(radius, n_neighbor)

    def forward(self, pos, centroids, feat=None):
        dev = pos.device
        group_idx = self.frnn(pos, centroids)
        B, N, _ = pos.shape
        glist = []
        for i in range(B):
            center = torch.zeros((N)).to(dev)
            center[centroids[i]] = 1
            src = group_idx[i].contiguous().view(-1)
            dst = centroids[i].view(-1, 1).repeat(1, self.n_neighbor).view(-1)

            unified = torch.cat([src, dst])
            uniq, inv_idx = torch.unique(unified, return_inverse=True)
            src_idx = inv_idx[:src.shape[0]]
            dst_idx = inv_idx[src.shape[0]:]

            g = dgl.graph((src_idx, dst_idx))
            g.ndata['pos'] = pos[i][uniq]
            g.ndata['center'] = center[uniq]
            if feat is not None:
                g.ndata['feat'] = feat[i][uniq]
            glist.append(g)
        bg = dgl.batch(glist)
        return bg


class RelativePositionMessage(nn.Module):
    '''
    Compute the input feature from neighbors
    '''
    def __init__(self, n_neighbor):
        super(RelativePositionMessage, self).__init__()
        self.n_neighbor = n_neighbor

    def forward(self, edges):
        pos = edges.src['pos'] - edges.dst['pos']
        if 'feat' in edges.src:
            res = torch.cat([pos, edges.src['feat']], 1)
        else:
            res = pos
        return {'agg_feat': res}