说明：  matlab编写的调整svm参数的程序，其中cross是主程序，另两个是自己编写的svm核函数，如果要用matlab自带的核函数就把-t的值改成2即可。Ytrain是标记矩阵，Xtrain是特征矩阵，都由用户自己导入。可利用k倍交叉验证来选择最优的c参数。k可自行更改。
(svm matlab prepared to adjust the parameters of the program, which cross the main program, and the other two are themselves prepared svm kernel function, if you use the value of the kernel function matlab own put-t can be changed to 2. Ytrain is labeled matrix, Xtrain is characteristic matrix, imported by the users themselves. K-fold cross-validation can be used to select the optimal c parameter. k can make changes.)