gbm <- gbm(formula, data=Mydata, distribution = "poisson",
                      var.monotone=rep(0,length=length(predictors)),
                      n.trees=10000, #3500
                      shrinkage=0.001,
                      interaction.depth=7,
                      train.fraction = .8,
                      n.cores=4,
                      keep.data=TRUE)