struct EvalPoissonNegLogLik : public EvalEWiseBase {

const char *Name() const override {

return "poisson-nloglik";

}

inline bst_float EvalRow(bst_float y, bst_float py) const {

const bst_float eps = 1e-16f;

if (py < eps) py = eps;

return common::LogGamma(y + 1.0f) + py - std::log(py) * y;

}

}

poisson_deviance <- function(y, py, eps) {

mean(LogGamma(y + 1.0f) + pmax(py, eps) - log(pmax(py, eps)) * y);

}

setinfo(xgbMatrix, "base_margin", log(exposure))

poisson_deviance <- function(y, py, exposure, eps) {

mean(LogGamma(y + 1.0f) + pmax(py + log(exposure), eps) - log(pmax(py +

log(exposure), eps)) * y);

}

poisson_deviance <- function(y, py) {mean(y*py - exp(py))}

2 * mean(y * log(y / py) - (y - py))