code: def generalized_kernel(
      x: Tensor,
      mat: Tensor,
      kernel: Callable = torch.nn.ReLU(),
      epsilon: float = 0.001,
  ) -> Tensor:
      batch_size, num_heads = x.size()[:2]
      projection = mat.t().expand(batch_size, num_heads, -1, -1)
      x = x @ projection
      out = kernel(x) + epsilon
      return out
  
file_path: pytorch_geometric/torch_geometric/nn/attention/performer.py
imports: import math
  from typing import Callable, Optional
  import torch
  from torch import Tensor
label_desc: Use image node_id 4 for calling a global function with example usage: generalized_kernel(x, mat, kernel, epsilon) and returns: out