求bloch方程的FID解得到磁矢量的变化规律，TXT文档中是Matlab的输入面板的程序代码，修改参数可以得到不同输入下的衰减规律。-FID Bloch equation solution to get the change law of magnetic vector, TXT documents is a Matlab program code input panel, modify the parameters can be obtained under different input