odes.py 文件源码

def _optimal_step_size(last_step,
                       error_ratio,
                       safety=0.9,
                       ifactor=10.0,
                       dfactor=0.2,
                       order=5,
                       name=None):
  """Calculate the optimal size for the next Runge-Kutta step."""
  with ops.name_scope(
      name, 'optimal_step_size', [last_step, error_ratio]) as scope:
    error_ratio = math_ops.cast(error_ratio, last_step.dtype)
    exponent = math_ops.cast(1 / order, last_step.dtype)
    # this looks more complex than necessary, but importantly it keeps
    # error_ratio in the numerator so we can't divide by zero:
    factor = math_ops.maximum(
        1 / ifactor,
        math_ops.minimum(error_ratio ** exponent / safety, 1 / dfactor))
    return math_ops.div(last_step, factor, name=scope)