输出2阶-7阶勒让德多项式的值，并分别写入data1-data6六个txt文件中，用origin绘制出2阶-7阶Legendre多项式图形-The output value of second-order Legendre polynomial-7 order, and were written data1-data6 six txt file, with origin draw the two bands-7 order Legendre polynomials graphics