YOLOv10改进 | 添加注意力机制篇 | 添加FocusedLinearAttention助力yolov10实现有效涨点（含二次创新PSA机制）

import torch.nn as nn
import torch
from einops import rearrange

__all__ = ['FocusedLinearAttention', 'C2f_FLA', 'PSAFLA']

class FocusedLinearAttention(nn.Module):
    def __init__(self, dim, num_patches=64, num_heads=8, qkv_bias=True, qk_scale=None, attn_drop=0.0, proj_drop=0.0,
                 sr_ratio=1,
                 focusing_factor=3.0, kernel_size=5):
        super().__init__()
        assert dim % num_heads == 0, f"dim {dim} should be divided by num_heads {num_heads}."
        self.dim = dim
        self.num_heads = num_heads
        head_dim = dim // num_heads

        self.q = nn.Linear(dim, dim, bias=qkv_bias)
        self.kv = nn.Linear(dim, dim * 2, bias=qkv_bias)
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim, dim)
        self.proj_drop = nn.Dropout(proj_drop)

        self.sr_ratio = sr_ratio
        if sr_ratio > 1:
            self.sr = nn.Conv2d(dim, dim, kernel_size=sr_ratio, stride=sr_ratio)
            self.norm = nn.LayerNorm(dim)

        self.focusing_factor = focusing_factor
        self.dwc = nn.Conv2d(in_channels=head_dim, out_channels=head_dim, kernel_size=kernel_size,
                             groups=head_dim, padding=kernel_size // 2)
        self.scale = nn.Parameter(torch.zeros(size=(1, 1, dim)))
        # self.positional_encoding = nn.Parameter(torch.zeros(size=(1, num_patches // (sr_ratio * sr_ratio), dim)))

    def forward(self, x):
        B, C, H, W = x.shape  # 输入为四维：[批次大小, 通道数, 高度, 宽度]
        dtype, device = x.dtype, x.device
        # 调整输入以匹配原始模块的预期格式
        x = rearrange(x, 'b c h w -> b (h w) c')
        q = self.q(x)
        if self.sr_ratio > 1:
            x_ = x.permute(0, 2, 1).reshape(B, C, H, W)
            x_ = self.sr(x_).reshape(B, C, -1).permute(0, 2, 1)
            x_ = self.norm(x_)
            kv = self.kv(x_).reshape(B, -1, 2, C).permute(2, 0, 1, 3)
        else:
            kv = self.kv(x).reshape(B, -1, 2, C).permute(2, 0, 1, 3)
        k, v = kv[0], kv[1]
        N = H * W  # 序列长度
        # 重新生成位置编码
        positional_encoding = nn.Parameter(torch.zeros(size=(1, N, self.dim), device=device))
        k = k + positional_encoding
        focusing_factor = self.focusing_factor
        kernel_function = nn.ReLU()
        scale = nn.Softplus()(self.scale)
        q = kernel_function(q) + 1e-6
        k = kernel_function(k) + 1e-6
        q = q / scale
        k = k / scale
        q_norm = q.norm(dim=-1, keepdim=True)
        k_norm = k.norm(dim=-1, keepdim=True)
        q = q ** focusing_factor
        k = k ** focusing_factor
        q = (q / q.norm(dim=-1, keepdim=True)) * q_norm
        k = (k / k.norm(dim=-1, keepdim=True)) * k_norm
        bool = False
        if dtype == torch.float16:
            q = q.float()
            k = k.float()
            v = v.float()
            bool = True
        q, k, v = (rearrange(x, "b n (h c) -> (b h) n c", h=self.num_heads) for x in [q, k, v])
        i, j, c, d = q.shape[-2], k.shape[-2], k.shape[-1], v.shape[-1]
        z = 1 / (torch.einsum("b i c, b c -> b i", q, k.sum(dim=1)) + 1e-6)
        if i * j * (c + d) > c * d * (i + j):
            kv = torch.einsum("b j c, b j d -> b c d", k, v)
            x = torch.einsum("b i c, b c d, b i -> b i d", q, kv, z)
        else:
            qk = torch.einsum("b i c, b j c -> b i j", q, k)
            x = torch.einsum("b i j, b j d, b i -> b i d", qk, v, z)
        if self.sr_ratio > 1:
            v = nn.functional.interpolate(v.permute(0, 2, 1), size=x.shape[1], mode='linear').permute(0, 2, 1)
        if bool:
            v = v.to(torch.float16)
            x = x.to(torch.float16)

        num = int(v.shape[1] ** 0.5)
        feature_map = rearrange(v, "b (w h) c -> b c w h", w=num, h=num)
        feature_map = rearrange(self.dwc(feature_map), "b c w h -> b (w h) c")
        x = x + feature_map
        x = rearrange(x, "(b h) n c -> b n (h c)", h=self.num_heads)

        x = self.proj(x)
        x = self.proj_drop(x)
        x = rearrange(x, 'b (h w) c -> b c h w', h=H, w=W)
        return x


def autopad(k, p=None, d=1):  # kernel, padding, dilation
    """Pad to 'same' shape outputs."""
    if d > 1:
        k = d * (k - 1) + 1 if isinstance(k, int) else [d * (x - 1) + 1 for x in k]  # actual kernel-size
    if p is None:
        p = k // 2 if isinstance(k, int) else [x // 2 for x in k]  # auto-pad
    return p


class Conv(nn.Module):
    """Standard convolution with args(ch_in, ch_out, kernel, stride, padding, groups, dilation, activation)."""
    default_act = nn.SiLU()  # default activation

    def __init__(self, c1, c2, k=1, s=1, p=None, g=1, d=1, act=True):
        """Initialize Conv layer with given arguments including activation."""
        super().__init__()
        self.conv = nn.Conv2d(c1, c2, k, s, autopad(k, p, d), groups=g, dilation=d, bias=False)
        self.bn = nn.BatchNorm2d(c2)
        self.act = self.default_act if act is True else act if isinstance(act, nn.Module) else nn.Identity()

    def forward(self, x):
        """Apply convolution, batch normalization and activation to input tensor."""
        return self.act(self.bn(self.conv(x)))

    def forward_fuse(self, x):
        """Perform transposed convolution of 2D data."""
        return self.act(self.conv(x))


class Bottleneck_FLA(nn.Module):
    """Standard bottleneck."""

    def __init__(self, c1, c2, shortcut=True, g=1, k=(3, 3), e=0.5):
        """Initializes a bottleneck module with given input/output channels, shortcut option, group, kernels, and
        expansion.
        """
        super().__init__()
        c_ = int(c2 * e)  # hidden channels
        self.cv1 = Conv(c1, c_, k[0], 1)
        self.cv2 = Conv(c_, c2, k[1], 1, g=g)
        self.FLA = FocusedLinearAttention(c_)
        self.add = shortcut and c1 == c2

    def forward(self, x):
        """'forward()' applies the YOLO FPN to input data."""
        return x + self.cv2(self.cv1(x)) if self.add else self.FLA(self.cv2(self.cv1(x)))


class C2f_FLA(nn.Module):
    """Faster Implementation of CSP Bottleneck with 2 convolutions."""

    def __init__(self, c1, c2, n=1, shortcut=False, g=1, e=0.5):
        """Initialize CSP bottleneck layer with two convolutions with arguments ch_in, ch_out, number, shortcut, groups,
        expansion.
        """
        super().__init__()
        self.c = int(c2 * e)  # hidden channels
        self.cv1 = Conv(c1, 2 * self.c, 1, 1)
        self.cv2 = Conv((2 + n) * self.c, c2, 1)  # optional act=FReLU(c2)
        self.m = nn.ModuleList(Bottleneck_FLA(self.c, self.c, shortcut, g, k=((3, 3), (3, 3)), e=1.0) for _ in range(n))

    def forward(self, x):
        """Forward pass through C2f layer."""
        x = self.cv1(x)
        x = x.chunk(2, 1)
        y = list(x)
        # y = list(self.cv1(x).chunk(2, 1))
        y.extend(m(y[-1]) for m in self.m)
        return self.cv2(torch.cat(y, 1))

    def forward_split(self, x):
        """Forward pass using split() instead of chunk()."""
        y = list(self.cv1(x).split((self.c, self.c), 1))
        y.extend(m(y[-1]) for m in self.m)
        return self.cv2(torch.cat(y, 1))


def autopad(k, p=None, d=1):  # kernel, padding, dilation
    """Pad to 'same' shape outputs."""
    if d > 1:
        k = d * (k - 1) + 1 if isinstance(k, int) else [d * (x - 1) + 1 for x in k]  # actual kernel-size
    if p is None:
        p = k // 2 if isinstance(k, int) else [x // 2 for x in k]  # auto-pad
    return p


class Conv(nn.Module):
    """Standard convolution with args(ch_in, ch_out, kernel, stride, padding, groups, dilation, activation)."""

    default_act = nn.SiLU()  # default activation

    def __init__(self, c1, c2, k=1, s=1, p=None, g=1, d=1, act=True):
        """Initialize Conv layer with given arguments including activation."""
        super().__init__()
        self.conv = nn.Conv2d(c1, c2, k, s, autopad(k, p, d), groups=g, dilation=d, bias=False)
        self.bn = nn.BatchNorm2d(c2)
        self.act = self.default_act if act is True else act if isinstance(act, nn.Module) else nn.Identity()

    def forward(self, x):
        """Apply convolution, batch normalization and activation to input tensor."""
        return self.act(self.bn(self.conv(x)))

    def forward_fuse(self, x):
        """Perform transposed convolution of 2D data."""
        return self.act(self.conv(x))

class PSAFLA(nn.Module):

    def __init__(self, c1, c2, e=0.5):
        super().__init__()
        assert (c1 == c2)
        self.c = int(c1 * e)
        self.cv1 = Conv(c1, 2 * self.c, 1, 1)
        self.cv2 = Conv(2 * self.c, c1, 1)

        self.attn = FocusedLinearAttention(self.c, num_patches=64, num_heads=self.c // 64)
        self.ffn = nn.Sequential(
            Conv(self.c, self.c * 2, 1),
            Conv(self.c * 2, self.c, 1, act=False)
        )

    def forward(self, x):
        a, b = self.cv1(x).split((self.c, self.c), dim=1)
        b = b + self.attn(b)
        b = b + self.ffn(b)
        return self.cv2(torch.cat((a, b), 1))

class Bottleneck_FLA(nn.Module):
    """Standard bottleneck."""

    def __init__(self, c1, c2, shortcut=True, g=1, k=(3, 3), e=0.5):
        """Initializes a bottleneck module with given input/output channels, shortcut option, group, kernels, and
        expansion.
        """
        super().__init__()
        c_ = int(c2 * e)  # hidden channels
        self.cv1 = Conv(c1, c_, k[0], 1)
        self.cv2 = Conv(c_, c2, k[1], 1, g=g)
        self.FLA = FocusedLinearAttention(c_)
        self.add = shortcut and c1 == c2

    def forward(self, x):
        """'forward()' applies the YOLO FPN to input data."""
        return x + self.cv2(self.cv1(x)) if self.add else self.FLA(self.cv2(self.cv1(x)))


class C2f_FLA(nn.Module):
    """Faster Implementation of CSP Bottleneck with 2 convolutions."""

    def __init__(self, c1, c2, n=1, shortcut=False, g=1, e=0.5):
        """Initialize CSP bottleneck layer with two convolutions with arguments ch_in, ch_out, number, shortcut, groups,
        expansion.
        """
        super().__init__()
        self.c = int(c2 * e)  # hidden channels
        self.cv1 = Conv(c1, 2 * self.c, 1, 1)
        self.cv2 = Conv((2 + n) * self.c, c2, 1)  # optional act=FReLU(c2)
        self.m = nn.ModuleList(Bottleneck_FLA(self.c, self.c, shortcut, g, k=((3, 3), (3, 3)), e=1.0) for _ in range(n))

    def forward(self, x):
        """Forward pass through C2f layer."""
        x = self.cv1(x)
        x = x.chunk(2, 1)
        y = list(x)
        # y = list(self.cv1(x).chunk(2, 1))
        y.extend(m(y[-1]) for m in self.m)
        return self.cv2(torch.cat(y, 1))

    def forward_split(self, x):
        """Forward pass using split() instead of chunk()."""
        y = list(self.cv1(x).split((self.c, self.c), 1))
        y.extend(m(y[-1]) for m in self.m)
        return self.cv2(torch.cat(y, 1))