support use objective name to create metric.

src/io/config.cpp

@@ -90,6 +90,13 @@ void GetMetricType(const std::unordered_map<std::string, std::string>& params, s
     }
     metric_types->shrink_to_fit();
   }
+  // add names of objective function if not providing metric
+  if (metric_types->empty()) {
+    if (ConfigBase::GetString(params, "objective", &value)) {
+      std::transform(value.begin(), value.end(), value.begin(), Common::tolower);
+      metric_types->push_back(value);
+    }
+  }
 }
 
 void GetTaskType(const std::unordered_map<std::string, std::string>& params, TaskType* task_type) {

src/metric/metric.cpp

@@ -9,11 +9,11 @@
 namespace LightGBM {
 
 Metric* Metric::CreateMetric(const std::string& type, const MetricConfig& config) {
-  if (type == std::string("l2") || type == std::string("mean_squared_error") || type == std::string("mse")) {
+  if (type == std::string("regression") || type == std::string("regression_l2") || type == std::string("l2") || type == std::string("mean_squared_error") || type == std::string("mse")) {
     return new L2Metric(config);
   } else if (type == std::string("l2_root") || type == std::string("root_mean_squared_error") || type == std::string("rmse")) {
     return new RMSEMetric(config);
-  } else if (type == std::string("l1") || type == std::string("mean_absolute_error") || type == std::string("mae")) {
+  } else if (type == std::string("regression_l1") || type == std::string("l1") || type == std::string("mean_absolute_error") || type == std::string("mae")) {
     return new L1Metric(config);
   } else if (type == std::string("quantile")) {
     return new QuantileMetric(config);
@@ -23,7 +23,7 @@ Metric* Metric::CreateMetric(const std::string& type, const MetricConfig& config
     return new FairLossMetric(config);
   } else if (type == std::string("poisson")) {
     return new PoissonMetric(config);
-  } else if (type == std::string("binary_logloss")) {
+  } else if (type == std::string("binary_logloss") || type == std::string("binary")) {
     return new BinaryLoglossMetric(config);
   } else if (type == std::string("binary_error")) {
     return new BinaryErrorMetric(config);
@@ -33,7 +33,7 @@ Metric* Metric::CreateMetric(const std::string& type, const MetricConfig& config
     return new NDCGMetric(config);
   } else if (type == std::string("map") || type == std::string("mean_average_precision")) {
     return new MapMetric(config);
-  } else if (type == std::string("multi_logloss")) {
+  } else if (type == std::string("multi_logloss") || type == std::string("multiclass") || type == std::string("multiclass_ova")) {
     return new MultiSoftmaxLoglossMetric(config);
   } else if (type == std::string("multi_error")) {
     return new MultiErrorMetric(config);

src/objective/objective_function.cpp

@@ -9,7 +9,8 @@ namespace LightGBM {
 
 ObjectiveFunction* ObjectiveFunction::CreateObjectiveFunction(const std::string& type, const ObjectiveConfig& config) {
   if (type == std::string("regression") || type == std::string("regression_l2")
-      || type == std::string("mean_squared_error") || type == std::string("mse")) {
+      || type == std::string("mean_squared_error") || type == std::string("mse") 
+      || type == std::string("l2_root") || type == std::string("root_mean_squared_error") || type == std::string("rmse")) {
     return new RegressionL2loss(config);
   } else if (type == std::string("regression_l1") || type == std::string("mean_absolute_error")  || type == std::string("mae")) {
     return new RegressionL1loss(config);