我正在使用LIBSVM编程进行一个简单的XOR分类，试图理解这些函数是如何工作的。我尽可能按照Readme中的说明设置了问题。然而，当使用svm_predict时，我得到的输出总是错误的（总是1或-1）。
在相关的问题中，有人建议问题可能出现在使用非常少的训练样本时。我尝试将样本数量增加到20，但这并没有帮助。
我怀疑问题出在prob.x和/或prob.y的定义上，但我无法理解具体是哪里。您能帮助澄清如何使用svm_node定义prob.x和prob.y吗？
我已经彻底搜索了但找不到答案…例如这里，这里，这里，这里，以及这里。
提前感谢！
这是我的代码：
//Parameterssvm_parameter param;param.svm_type = C_SVC;param.kernel_type = RBF;param.degree = 3;param.gamma = 0;param.coef0 = 0;param.nu = 0.5;param.cache_size = 100;param.C = 0.4;param.eps = 1e-3;param.p = 0.1;param.shrinking = 1;param.probability = 0;param.nr_weight = 0;param.weight_label = NULL;param.weight = NULL;//Problem definitionsvm_problem prob;//Lengthprob.l = 4; //number of training examples//x valuessvm_node** x = new svm_node *[prob.l]; //Array of pointers to pointers to arrayssvm_node* x_space1 = new svm_node[3]; //Fist training examplesvm_node* x_space2 = new svm_node[3]; //Second training examplesvm_node* x_space3 = new svm_node[3]; //Third training examplesvm_node* x_space4 = new svm_node[3]; //Fourth training examplex_space1[0].index = 1; //Fist training examplex_space1[0].value = 1;x_space1[1].index = 2;x_space1[1].value = 1;x_space1[2].index = -1;x_space2[0].index = 1; //Second training examplex_space2[0].value = 1;x_space2[1].index = 2;x_space2[1].value = 0;x_space2[2].index = -1;x_space3[0].index = 1; //Third training examplex_space3[0].value = 0;x_space3[1].index = 2;x_space3[1].value = 1;x_space3[2].index = -1;x_space4[0].index = 1; //Fourth training examplex_space4[0].value = 0;x_space4[1].index = 2;x_space4[1].value = 0;x_space4[2].index = -1;x[0] = x_space1; //Set each training example to xx[1] = x_space2;x[2] = x_space3;x[3] = x_space4;prob.x = x; //Assign x to the struct field prob.x//yvaluesprob.y = new double[prob.l];prob.y[0] = -1;prob.y[1] = 1;prob.y[2] = 1;prob.y[3] = -1;//Train modelsvm_model *model = svm_train(&prob,¶m);//Test modelsvm_node* testnode = new svm_node[3];testnode[0].index = 1;testnode[0].value = 1;testnode[1].index = 2;testnode[1].value = 0;testnode[2].index = -1;double retval = svm_predict(model,testnode);qDebug()<<retval; //Should return +1 but returns -1回答：
看起来是你的参数出了问题。例如，如果你使用RBF核，param.gamma不应该为零。
