cross.validation: cross validation
In sbbrandt/xgbAnalysis: Reaction coordinates analysis

calculates cross validation for given parameter

1 2	cross.validation(pre = "", nfold, nthread, nrounds, testparname = NA, testpar = NA, plot = T, pdim = 10, width = 1.5)

`nfold`	how many folds of dataset
`nthread`	number of CPU cores to use, NA for all
`nrounds`	number of training rounds
`plot`	should results be plotted, default=TRUE
`pdim`	dimension of plot, default=10
`width`	proportion of width to height, default=1.5
`defpar`	default parameter:default = list(eta=0.3, gamma=0, max_depth=6, min_child_weight=1, subsample=1, colsample_bytree=1)