[R] How to personalize the rpart function: t.default(x)

[Simone Vantini]

I'm trying to personalize the rpart function by introducing a
list('init','split','eval') in the argument method. But I receive an error
message:"Error in t.default(x): argument is not a matrix".
Can anyone tell me what the argument of this function is or where this
function appears in the rpart function.Thanks Simone Vantini