class_docstr: Progressive Neural Network layer.
  
  The adaptation phase assumes that each experience is a separate task.
  Multiple experiences with the same task label or multiple task labels
  within the same experience will result in a runtime error.
docstr: Add a new column.
docstr_tok: ["Add","a","new","column","."]
code: def _add_column(self):
      """Add a new column."""
      # Freeze old parameters
      for param in self.parameters():
          param.requires_grad = False
      self.columns.append(
          PNNColumn(
              self.in_features,
              self.out_features_per_column,
              self.num_columns,
              adapter=self.adapter,
          )
      )
  
imports: import torch
  import torch.nn.functional
  from torch import nn
  from avalanche.benchmarks.utils.flat_data import ConstantSequence
  from avalanche.models import MultiTaskModule
  from avalanche.models import MultiHeadClassifier
  from avalanche.benchmarks.scenarios import CLExperience
label_desc: Use image node_id 4 for calling the PNNLayer obj's underlying member method code with example usage: obj._add_column() without return types