说明：  test1.txt 第一列为时间t，0.001s为步长；第二列为系统的输入信号；第三列为系统的输出信号。 signal_analyzer.m首先将test1.txt 的数据读入workspace，然后进行FFT，分析出两信号的频率，输出对于输入的幅值衰减（db），输出对输入的相位差。
(test1.txt the first time as t, 0.001s for the step the second as the system input signal the third as the system output signal. signal_analyzer.m first test1.txt data read workspace, and then proceed to FFT, analysis of the two signals in the frequency, the output for input amplitude attenuation (db), the output of the input phase difference.)