class_docstr: Implementation Focal cosine loss from the "Data-Efficient Deep Learning Method for Image Classification
  Using Data Augmentation, Focal Cosine Loss, and Ensemble" (https://arxiv.org/abs/2007.07805).
  
  Credit: https://www.kaggle.com/c/cassava-leaf-disease-classification/discussion/203271
code: def __init__(
      self,
      alpha: float = 1,
      gamma: float = 2,
      xent: float = 0.1,
      reduction="mean",
  ):
      super(FocalCosineLoss, self).__init__()
      self.alpha = alpha
      self.gamma = gamma
      self.xent = xent
      self.reduction = reduction
  
imports: from typing import Optional
  from torch import nn, Tensor
  import torch.nn.functional
  import torch
label_desc: Use image node_id 1 to create a new FocalCosineLoss object from inherited base classes: nn with example: obj = FocalCosineLoss(alpha, gamma, xent, reduction)