private double[] toArray(List<Double> valueList) {
        double[] valueArray = new double[valueList.size()];
        for (int i = 0; i < valueList.size(); i++) {
            valueArray[i] = valueList.get(i);
        }
        return valueArray;
    }
Optimize the given node, if it is the root of a gdbt forest. Otherwise do nothing and return false
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestOptimizer.java