在有限元的计算中，常需要用到三角形区域上的积分，以及右端函数和基函数乘后的积分，本代码中以上两种均可计算，可精确到想要求的精度-Finite element calculations, often require the integration on the triangle area, as well as the right end of the function and the basis function multiplied Points, this code can calculate the above two, can be accurate to want to the required accuracy