调谐器插入符号长度

我在跟踪一个 caret 使用 Sonar 内置数据集。该数据集由208行和61个特征/变量组成(如果该类被丢弃,则为60个)。

在一个步骤中,它解释了 trainControl 和 train 功能如下:

# Model training controller (cross-validation with 3 reps)
control <- trainControl(method="repeatedcv", repeats=3)

myModel <- train (Class ~ ., 
           data=train_partition,
           method="pls",
           preProc=c("scale"),
           trControl=control,
           tuneLength=3)

当我展示 火车 文档 tuneLength 参数指定为:

An integer denoting the amount of granularity in the tuning parameter grid. 
By default, this argument is the number of levels for each tuning parameters that 
should be generated by train. If trainControl has the option search = "random", 
this is the maximum number of tuning parameter combinations that will be generated 
by the random search. (NOTE: If given, this argument must be named.)

文件第一行中规定的“pls”方法的“调整参数”是什么?