正则表达式高手请来帮帮忙 谢谢
string s=@"Sum(x1 , x2, Sum(x3 , x4) + Sum(x5 , x6, (x7 + x8 )*x9))+ Sum(x1 , x2,Sum(x3 , x4)+Sum(x5 , x6))+ Sum(x1,x2,Sum( x3,x4) + Sum(x5,x6,( x7 + x8 )* x9))";

说明：正则表达式中的x1,x2.....为函数的参数


用一个正则表达式 匹配出所有函数
例如：匹配结果1：Sum(x1 , x2, Sum(x3 , x4) + Sum(x5 , x6, (x7 + x8 )*x9))
匹配结果2：Sum(x1 , x2,Sum(x3 , x4)+Sum(x5 , x6))
匹配结构3：Sum(x1,x2,Sum( x3,x4) + Sum(x5,x6,( x7 + x8 )* x9))
[解决办法]
Sum\(((?<o>\()
[解决办法]
(?<-o>)\)
[解决办法]
[^()]+)*(?(o)(?!))\)