这段代码定义了三个函数：
get_stock_data: Retrieves historical stock data for a given ticker using the yahoo finance library.
meets_criteria: Determines whether a stock meets the buy or short criteria based on the current price and the previous closing price.
trading_strategy: Implements the main trading strategy. It loops through the trading day and executes trades based on the buy and short criteria, as well as the 1% decline and increase thresholds. It closes all positions at the end of the trading day.