matrix displacement method

代码说明：

  使用矩阵位移法做平面杆件结构静力计算； 与龙驭球《结构力学》中介绍的方法一致，可帮助土木工程专业学习矩阵位移法时检验中间过程；(The matrix displacement method is used to calculate the static force of planar bar structure. Consistent with the method introduced in the "structural mechanics" of long chien ball, it can help civil engineering majors to learn the matrix displacement method to test the intermediate process.)