帮助文档内容：
SETDIFF(A,B) when A and B are vectors returns the values
in A that are not in B. The result will be sorted. A and B
can be cell arrays of strings.
SETDIFF(A,B,‘rows‘) when A are B are matrices with the same
number of columns returns the rows from A that are not in B.
理解：
matlab中setdiff（）函数作用：判断2个数组中不同元素
c = setdiff(A, B)当A和B是具有相同列数的矩阵时，返回A中有而B中没有的那些行。
原文：http://blog.csdn.net/u013476464/article/details/42610433