功能: 求解对称带状矩阵方程

格式: SparseSolveSym(A, B)

A : 带状系数矩阵
B : 一个与A行数一致的矩阵变量

说明:
1. 本函数主要求解如下线性方程组里的X
$$
AX = B
$$
由于A对称，因此函数里的A约定只存储上带宽部分

2. B参数如果有多列，每一列单独进行求解

3. 当矩阵A分解失败时,本函数内部会采用拟牛顿法进行求解。

例子:
已知如下A,b
$$
\begin{cases}
A&=\begin{bmatrix}
10.886&-0.452059&-9.67399
\\
-0.452059&4.12387&-5.14226&6.78224
\\
-9.67399&-5.14226&-11.6086&2.2528&-1.99543
\\
&6.78224&2.2528&-6.52699&7.83059&3.26454
\\
&&-1.99543&7.83059&-6.93393&7.80465&-4.66669
\\
&&&3.26454&7.80465&-4.83543&0.795207&4.41905&0
\\
&&&&-4.66669&0.795207&-3.99338&-4.31413&-5.42064
\\
&&&&&4.41905&-4.31413&7.6331&7.86745&6.29534
\\
&&&&&&-5.42064&7.86745&-4.78847&3.68437
\\
&&&&&&&6.29534&3.68437&13.1511
\end{bmatrix}
\\
\\
\mathbf{b}&=\begin{bmatrix}-0.350187&-5.6835&9.00505&8.40257&-7.0468&7.62124&2.82161&-1.36093&2.39193&-4.37881\end{bmatrix}^T
\end{cases}
$$

b = [-0.350187;-5.6835;9.00505;8.40257;-7.0468;7.62124;2.82161;-1.36093;2.39193;-4.37881];
a = [ 10.8860000000000   -0.45205900000000   -9.67399000000000
      4.12387000000000   -5.14226000000000    6.78224000000000
     -11.6086000000000    2.25280000000000   -1.99543000000000
     -6.52699000000000    7.83059000000000    3.26454000000000
     -6.93393000000000    7.80465000000000   -4.66669000000000
     -4.83543000000000    0.79520700000000    4.41905000000000
     -3.99338000000000   -4.31413000000000   -5.42064000000000
      7.63310000000000    7.86745000000000    6.29534000000000
     -4.78847000000000    3.68437000000000    0.00000000000000
      13.1511000000000    0.00000000000000    0.00000000000000 ];
x = SparseSolveSym(a, b)//执行得到如下结果
x =
[-0.35727689175291
 -1.27448364205052
 -0.30628390590443
 -0.31909765143112
  1.92521586432883
  0.17708376822250
 -1.45884770371484
 -0.98354326772200
 -0.29448747918871
  0.22035648034914 ]