采用理查森外推法计算标量函数梯度的程序(很容易改写为计算雅克比矩阵)，算例为sin(x)+cos(y)。richarson(fun,x0)中，h是初始步长，j是迭代次数，精度是2*j+2阶。-Scalar function gradient procedures using Richardson extrapolation method, in the function richarson (fun, x0), h is the initial step, j is the number of iterations, precision is 2* j+2 order.