write a transformer model with pytorch

def transformer(d_model, nhead, num_encoder_layers, num_decoder_layers, dim_feedforward, dropout, activation):
  return nn.Transformer(d_model, nhead, num_encoder_layers, num_decoder_layers, dim_feedforward, dropout, activation)
    
transformer(512, 8, 6, 6, 2048, 0.2, 'relu')