import math


def linear_learning_rate(num_linear_feature_columns):
    """Returns the default learning rate of the linear model.
    The calculation is a historical artifact of this initial implementation, but
    has proven a reasonable choice.
    Args:
      num_linear_feature_columns: The number of feature columns of the linear model.
    Returns:
      A float.
    """
    default_learning_rate = 1. / math.sqrt(num_linear_feature_columns)
    return min(0.005, default_learning_rate)