我想比较标准的神经网络方法发挥到了极致学习机分类器（基于ROC指标），使用方法"nnet"，并"elm"在R包caret。对于nnet，一切正常，但是使用时method = "elm"出现以下错误：
Error in evalSummaryFunction(y, wts = weights, ctrl = trControl, lev = classLevels, :
train()'s use of ROC codes requires class probabilities. See the classProbs option of trainControl()
In addition: Warning messages:
1: In train.default(x, y, weights = w, ...) :
At least one of the class levels are not valid R variables names; This may cause errors if class probabilities are generated because the variables names will be converted …