def update_tr_radius(Delta, actual_reduction, predicted_reduction, step_norm, bound_hit):
 if (predicted_reduction > 0):
  ratio = (actual_reduction / predicted_reduction)
 else:
  ratio = 0
 if (ratio < 0.25):
  Delta = (0.25 * step_norm)
 elif ((ratio > 0.75) and bound_hit):
  Delta *= 2.0
 return (Delta, ratio)

def update_tr_radius ( Delta , actual_reduction , predicted_reduction , step_norm , bound_hit ) : if ( predicted_reduction > 0 ) : ratio = ( actual_reduction / predicted_reduction ) else : ratio = 0 if ( ratio < 0.25 ) : Delta = ( 0.25 * step_norm ) elif ( ( ratio > 0.75 ) and bound_hit ) : Delta *= 2.0 return ( Delta , ratio )
update the radius of a trust region based on the cost reduction .