pickSizeTolerance(x, metric, tol = 1.5, maximize) 
pickSizeBest(x, metric, maximize) pickVars(y, size) 
caretFuncs
lmFuncs
rfFuncs
treebagFuncs
ldaFuncs
nbFuncs
Overall and varfunctions argument of rfeControl. See rfeControl for details on how these functions should be defined.
rfeControl, rfe