diff --git a/.ci/ci.yaml b/.ci/ci.yaml
index 739ba9906c..e0654b49e1 100644
--- a/.ci/ci.yaml
+++ b/.ci/ci.yaml
@@ -57,23 +57,6 @@ jobs:
   steps:
   - template: macos-steps.yaml
 
-- job: WindowsVS14
-  timeoutInMinutes: 360
-  displayName: Windows VS14
-  pool:
-    vmImage: vs2015-win2012r2
-  strategy:
-    matrix:
-      Plain:
-        CMakeArgs: '-DDEBUG=ON -DPROFILE=OFF -DBUILD_PYTHON_BINDINGS=OFF'
-        CMakeGenerator: '-G "Visual Studio 14 2015 Win64"'
-        MSBuildVersion: '14.0'
-        ArchiveNoLibs: 'mlpack-windows-vs14-no-libs.zip'
-        ArchiveLibs: 'mlpack-windows-vs14.zip'
-        ArchiveTests: 'mlpack_test-vs14.xml'
-  steps:
-  - template: windows-steps.yaml
-
 - job: WindowsVS15
   timeoutInMinutes: 360
   displayName: Windows VS15
diff --git a/COPYRIGHT.txt b/COPYRIGHT.txt
index ce5c944e0d..db423bb3b8 100644
--- a/COPYRIGHT.txt
+++ b/COPYRIGHT.txt
@@ -130,6 +130,7 @@ Copyright:
   Copyright 2020, Saraansh Tandon <saraanshtandon1999@gmail.com>
   Copyright 2020, Gaurav Singh <gs8763076@gmail.com>
   Copyright 2020, Lakshya Ojha <ojhalakshya@gmail.com>
+  Copyright 2020, Bisakh Mondal <bisakhmondal00@gmail.com>
 
 License: BSD-3-clause
   All rights reserved.
diff --git a/HISTORY.md b/HISTORY.md
index c93dcba0eb..bcd3e5fac6 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,9 @@
 ### mlpack ?.?.?
 ###### ????-??-??
+  * Templated return type of `Forward function` of loss functions (#2339).
+  
+  * Added `R2 Score` regression metric (#2323).
+
   * Added `mean squared logarithmic error` loss function for neural networks
     (#2210).
 
diff --git a/doc/tutorials/reinforcement_learning/reinforcement_learning.txt b/doc/tutorials/reinforcement_learning/reinforcement_learning.txt
index 1c837ef070..a91dc27671 100644
--- a/doc/tutorials/reinforcement_learning/reinforcement_learning.txt
+++ b/doc/tutorials/reinforcement_learning/reinforcement_learning.txt
@@ -1,6 +1,7 @@
 /*!
 @file rl.txt
 @author Sriram S K
+@author Joel Joseph
 @brief Tutorial for how to use the Reinforcement Learning module in mlpack.
 
 @page rltutorial Reinforcement Learning Tutorial
@@ -29,6 +30,7 @@ This tutorial is split into the following sections:
  - \ref environment_rltut
  - \ref agent_components_rltut
  - \ref q_learning_rltut
+ - \ref async_learning_rltut
  - \ref further_rltut
 
 @section environment_rltut Reinforcement Learning Environments
@@ -231,9 +233,167 @@ to have converged when the average return reaches a predetermined value (i.e. >
 Conversely, if the average return does not go beyond that amount even after a thousand 
 episodes, we can conclude that the agent will not converge and exit the training loop.
 
+@section async_learning_rltut
+
+In 2016, Researchers at Deepmind and University of Montreal published their paper 
+"Asynchronous Methods for Deep Reinforcement Learning". In it they described asynchronous
+variants of four standard reinforcement learning algorithms:
+	- One-Step SARSA
+	- One-Step Q-Learning
+	- N-Step Q-Learning
+	- Advantage Actor-Critic(A3C)
+
+Online RL algorithms and Deep Neural Networks make an unstable combination because of the
+non-stationary and correlated nature of online updates. Although this is solved by Experience Replay,
+it has several drawbacks: it uses more memory and computation per real interaction; and it requires 
+off-policy learning algorithms.
+
+Asynchronous methods, instead of experience replay, asynchronously executes multiple agents
+in parallel, on multiple instances of the environment, which solves all the above problems.
+
+Here, we demonstrate Asynchronous Learning methods in mlpack through the training of an async
+agent. Asynchronous learning involves training several agents simultaneously. Here, each of the
+agents are referred to as "workers". Currently mlpack has One-Step Q-Learning worker, N-Step 
+Q-Learning worker and One-Step SARSA worker.
+
+Let's examine the sample code in chunks.
+
+Apart from the includes used for the q-learning example, two more have to be included:
+
+@code
+#include <mlpack/methods/reinforcement_learning/async_learning.hpp>
+#include <mlpack/methods/reinforcement_learning/policy/aggregated_policy.hpp>
+@endcode
+
+Here we don't use experience replay, and instead of a single policy, we use three different
+policies, each corresponding to its worker. Number of workers created, depends on the number of 
+policies given in the Aggregated Policy. The column vector contains the probability distribution 
+for each child policy. We should make sure its size is same as the number of policies and the sum
+of its elements is equal to 1.
+
+@code
+AggregatedPolicy<GreedyPolicy<CartPole>> policy({GreedyPolicy<CartPole>(0.7, 5000, 0.1),
+                                                 GreedyPolicy<CartPole>(0.7, 5000, 0.01),
+                                                 GreedyPolicy<CartPole>(0.7, 5000, 0.5)},
+                                                 arma::colvec("0.4 0.3 0.3"));
+@endcode
+
+Now, we will create the "OneStepQLearning" agent. We could have used "NStepQLearning" or "OneStepSarsa"
+here according to our requirement.
+
+@code
+OneStepQLearning<CartPole, decltype(model), ens::AdamUpdate, decltype(policy)>
+    agent(std::move(config), std::move(model), std::move(policy));
+@endcode
+
+Here, unlike the Q-Learning example, instead of the entire while loop, we use the Train method of the Asynchronous
+Learning class inside a for loop. 100 training episodes will take around 50 seconds.
+
+@code
+for (int i = 0; i < 100; i++)
+{
+  agent.Train(measure);
+}
+@endcode
+
+What is "measure" here? It is a lambda function which returns a boolean value (indicating the end of training)
+and accepts the episode return (total reward of a deterministic test episode) as parameter.
+So, let's create that.
+
+@code
+arma::vec returns(20, arma::fill::zeros);
+size_t position = 0;
+size_t episode = 0;
+
+auto measure = [&returns, &position, &episode](double episodeReturn)
+{
+  if(episode > 10000) return true;
+
+  returns[position++] = episodeReturn;
+  position = position % returns.n_elem;
+  episode++;
+
+  std::cout << "Episode No.: " << episode 
+      << "; Episode Return: " << episodeReturn 
+      << "; Average Return: " << arma::mean(returns) << endl;
+};
+@endcode
+
+This will train three different agents on three CPU threads asynchronously and use this data to update the
+action value estimate.
+Voila, thats all there is to it. 
+
+Here is the full code to try this right away:
+
+@code
+#include <mlpack/core.hpp>
+#include <mlpack/methods/ann/ffn.hpp>
+#include <mlpack/methods/ann/init_rules/gaussian_init.hpp>
+#include <mlpack/methods/ann/layer/layer.hpp>
+#include <mlpack/methods/ann/loss_functions/mean_squared_error.hpp>
+#include <mlpack/methods/reinforcement_learning/async_learning.hpp>
+#include <mlpack/methods/reinforcement_learning/environment/cart_pole.hpp>
+#include <mlpack/methods/reinforcement_learning/policy/greedy_policy.hpp>
+#include <mlpack/methods/reinforcement_learning/policy/aggregated_policy.hpp>
+#include <mlpack/methods/reinforcement_learning/training_config.hpp>
+#include <ensmallen.hpp>
+
+using namespace mlpack;
+using namespace mlpack::ann;
+using namespace mlpack::rl;
+int main()
+{
+  // Set up the network.
+  FFN<MeanSquaredError<>, GaussianInitialization> model(MeanSquaredError<>(), GaussianInitialization(0, 0.001));
+  model.Add<Linear<>>(4, 128);
+  model.Add<ReLULayer<>>();
+  model.Add<Linear<>>(128, 128);
+  model.Add<ReLULayer<>>();
+  model.Add<Linear<>>(128, 2);
+
+  AggregatedPolicy<GreedyPolicy<CartPole>> policy({GreedyPolicy<CartPole>(0.7, 5000, 0.1),
+                                                   GreedyPolicy<CartPole>(0.7, 5000, 0.01),
+                                                   GreedyPolicy<CartPole>(0.7, 5000, 0.5)},
+                                                   arma::colvec("0.4 0.3 0.3"));
+
+  TrainingConfig config;
+  config.StepSize() = 0.01;
+  config.Discount() = 0.9;
+  config.TargetNetworkSyncInterval() = 100;
+  config.ExplorationSteps() = 100;
+  config.DoubleQLearning() = false;
+  config.StepLimit() = 200;
+
+  OneStepQLearning<CartPole, decltype(model), ens::VanillaUpdate, decltype(policy)>
+      agent(std::move(config), std::move(model), std::move(policy));
+
+  arma::vec returns(20, arma::fill::zeros);
+  size_t position = 0;
+  size_t episode = 0;
+
+  auto measure = [&returns, &position, &episode](double episodeReturn)
+  {
+    if(episode > 10000) return true;
+
+    returns[position++] = episodeReturn;
+    position = position % returns.n_elem;
+    episode++;
+
+    std::cout << "Episode No.: " << episode 
+        << "; Episode Return: " << episodeReturn 
+        << "; Average Return: " << arma::mean(returns) << endl;
+  };
+
+  for (int i = 0; i < 100; i++)
+  {
+    agent.Train(measure);
+  }
+}
+@endcode
+
 @section further_rltut Further documentation
 
 For further documentation on the rl classes, consult the \ref mlpack::rl
 "complete API documentation".
 
-*/
\ No newline at end of file
+*/
diff --git a/src/mlpack/core/cv/metrics/CMakeLists.txt b/src/mlpack/core/cv/metrics/CMakeLists.txt
index 4cf1027874..b9edacaf9a 100644
--- a/src/mlpack/core/cv/metrics/CMakeLists.txt
+++ b/src/mlpack/core/cv/metrics/CMakeLists.txt
@@ -13,6 +13,8 @@ set(SOURCES
   precision_impl.hpp
   recall.hpp
   recall_impl.hpp
+  r2_score.hpp
+  r2_score_impl.hpp
 )
 
 # Add directory name to sources.
diff --git a/src/mlpack/core/cv/metrics/r2_score.hpp b/src/mlpack/core/cv/metrics/r2_score.hpp
new file mode 100644
index 0000000000..6fcac955aa
--- /dev/null
+++ b/src/mlpack/core/cv/metrics/r2_score.hpp
@@ -0,0 +1,76 @@
+/**
+ * @file r2_score.hpp
+ * @author Bisakh Mondal
+ *
+ * The R^2 (Coefficient of determination) regression metric.
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+#ifndef MLPACK_CORE_CV_METRICS_R2SCORE_HPP
+#define MLPACK_CORE_CV_METRICS_R2SCORE_HPP
+
+#include <mlpack/core.hpp>
+
+namespace mlpack {
+namespace cv {
+
+/**
+ * The R2 Score is a metric of performance for regression algorithms
+ * that represents the proportion of variance (here y) that has been
+ * explained by the independent variables in the model. It provides
+ * an indication of goodness of fit and therefore a measure of how
+ * well unseen samples are likely to be predicted by the model,
+ * through the proportion of explained variance.
+ * As R2 Score is dataset dependent it can have wide range of values. The
+ * best possible score is @f$R^2 =1.0@f$. Values of R2 outside the range
+ * 0 to 1 can occur when the model fits the data worse than a horizontal
+ * hyperplane. This would occur when the wrong model was chosen, or
+ * nonsensical constraints were applied by mistake. A model which
+ * predicts exactly the expected value of y, disregarding the input
+ * features, gets a R2 Score equals to 0.0.
+ * If a model predicts @f$ \hat{y}_i $@f of the @f$ i $@f-th sample for a true
+ * @f$ y_i $@f for total n samples, the R2 Score is calculated by
+ * @f{eqnarray*}{
+ * R^{2} \left( y, \hat{y} \right) &=& 1-\frac{\sum_{i=1}^{n}
+ *    \left( y_i - \hat{y_i} \right)^2 }
+ *    {\sum_{i=1}^{n} \left( y_i - \bar{y}\right)^2}\\
+ * @f}
+ * 
+ * where @f$ \bar{y} = frac{1}{y}\sum_{i=1}^{n} y_i $@f.
+ * For example, a model having R2Score = 0.85, explains 85 \% variability of
+ * the response data around its mean.
+ */
+class R2Score
+{
+ public:
+  /**
+   * Run prediction and calculate the R squared error.
+   *
+   * @param model A regression model.
+   * @param data Column-major data containing test items.
+   * @param responses Ground truth (correct) target values for the test items,
+   *     should be either a row vector or a column-major matrix.
+   * @return calculated R2 Score.
+   */
+  template<typename MLAlgorithm, typename DataType, typename ResponsesType>
+  static double Evaluate(MLAlgorithm& model,
+                         const DataType& data,
+                         const ResponsesType& responses);
+
+  /**
+   * Information for hyper-parameter tuning code. It indicates that we want
+   * to maximize the measurement.
+   */
+  static const bool NeedsMinimization = false;
+};
+
+} // namespace cv
+} // namespace mlpack
+
+// Include implementation.
+#include "r2_score_impl.hpp"
+
+#endif
diff --git a/src/mlpack/core/cv/metrics/r2_score_impl.hpp b/src/mlpack/core/cv/metrics/r2_score_impl.hpp
new file mode 100644
index 0000000000..86c57e11fb
--- /dev/null
+++ b/src/mlpack/core/cv/metrics/r2_score_impl.hpp
@@ -0,0 +1,55 @@
+/**
+ * @file r2_score_impl.hpp
+ * @author Bisakh Mondal
+ *
+ * The implementation of the class R2Score.
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+#ifndef MLPACK_CORE_CV_METRICS_R2SCORE_IMPL_HPP
+#define MLPACK_CORE_CV_METRICS_R2SCORE_IMPL_HPP
+
+namespace mlpack {
+namespace cv {
+
+template<typename MLAlgorithm, typename DataType, typename ResponsesType>
+double R2Score::Evaluate(MLAlgorithm& model,
+                         const DataType& data,
+                         const ResponsesType& responses)
+{
+  if (data.n_cols != responses.n_cols)
+  {
+    std::ostringstream oss;
+    oss << "R2Score::Evaluate(): number of points (" << data.n_cols << ") "
+        << "does not match number of responses (" << responses.n_cols << ")!"
+        << std::endl;
+    throw std::invalid_argument(oss.str());
+  }
+
+  ResponsesType predictedResponses;
+  // Taking Predicted Output from the model.
+  model.Predict(data, predictedResponses);
+  // Mean value of response.
+  double meanResponses = arma::mean(responses);
+
+  // Calculate the numerator i.e. residual sum of squares.
+  double residualSumSquared = arma::accu(arma::square(responses -
+      predictedResponses));
+
+  // Calculate the denominator i.e.total sum of squares.
+  double totalSumSquared = arma::accu(arma::square(responses - meanResponses));
+
+  // Handling undefined R2 Score when both denominator and numerator is 0.0.
+  if (residualSumSquared == 0.0)
+    return totalSumSquared ? 1.0 : DBL_MIN;
+
+  return 1 - residualSumSquared / totalSumSquared;
+}
+
+} // namespace cv
+} // namespace mlpack
+
+#endif
diff --git a/src/mlpack/methods/ann/loss_functions/cross_entropy_error.hpp b/src/mlpack/methods/ann/loss_functions/cross_entropy_error.hpp
index 3041ae3099..1811f99998 100644
--- a/src/mlpack/methods/ann/loss_functions/cross_entropy_error.hpp
+++ b/src/mlpack/methods/ann/loss_functions/cross_entropy_error.hpp
@@ -49,7 +49,8 @@ class CrossEntropyError
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/cross_entropy_error_impl.hpp b/src/mlpack/methods/ann/loss_functions/cross_entropy_error_impl.hpp
index 9c6d73e481..7d0d80357b 100644
--- a/src/mlpack/methods/ann/loss_functions/cross_entropy_error_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/cross_entropy_error_impl.hpp
@@ -27,8 +27,10 @@ CrossEntropyError<InputDataType, OutputDataType>::CrossEntropyError(
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double CrossEntropyError<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+CrossEntropyError<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   return -arma::accu(target % arma::log(input + eps) +
       (1. - target) % arma::log(1. - input + eps));
diff --git a/src/mlpack/methods/ann/loss_functions/dice_loss.hpp b/src/mlpack/methods/ann/loss_functions/dice_loss.hpp
index a30618e424..42551388aa 100644
--- a/src/mlpack/methods/ann/loss_functions/dice_loss.hpp
+++ b/src/mlpack/methods/ann/loss_functions/dice_loss.hpp
@@ -62,7 +62,8 @@ class DiceLoss
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/dice_loss_impl.hpp b/src/mlpack/methods/ann/loss_functions/dice_loss_impl.hpp
index 708c1102f7..904d699c21 100644
--- a/src/mlpack/methods/ann/loss_functions/dice_loss_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/dice_loss_impl.hpp
@@ -27,8 +27,9 @@ DiceLoss<InputDataType, OutputDataType>::DiceLoss(
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double DiceLoss<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type DiceLoss<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   return 1 - ((2 * arma::accu(target % input) + smooth) /
     (arma::accu(target % target) + arma::accu(
diff --git a/src/mlpack/methods/ann/loss_functions/earth_mover_distance.hpp b/src/mlpack/methods/ann/loss_functions/earth_mover_distance.hpp
index 0683715bd4..71c0aa8e4b 100644
--- a/src/mlpack/methods/ann/loss_functions/earth_mover_distance.hpp
+++ b/src/mlpack/methods/ann/loss_functions/earth_mover_distance.hpp
@@ -45,7 +45,8 @@ class EarthMoverDistance
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/earth_mover_distance_impl.hpp b/src/mlpack/methods/ann/loss_functions/earth_mover_distance_impl.hpp
index 9ba7ac8f47..44d5e24c4e 100644
--- a/src/mlpack/methods/ann/loss_functions/earth_mover_distance_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/earth_mover_distance_impl.hpp
@@ -26,8 +26,10 @@ EarthMoverDistance<InputDataType, OutputDataType>::EarthMoverDistance()
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double EarthMoverDistance<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+EarthMoverDistance<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   return -arma::accu(target % input);
 }
diff --git a/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss.hpp b/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss.hpp
index bcb9b17d6d..3e3eac19ec 100644
--- a/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss.hpp
+++ b/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss.hpp
@@ -48,7 +48,8 @@ class HingeEmbeddingLoss
    * @param target Target data to compare with.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss_impl.hpp b/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss_impl.hpp
index b0e71632cb..f3f420b3ca 100644
--- a/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/hinge_embedding_loss_impl.hpp
@@ -27,8 +27,10 @@ HingeEmbeddingLoss<InputDataType, OutputDataType>::HingeEmbeddingLoss()
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double HingeEmbeddingLoss<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+HingeEmbeddingLoss<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   TargetType temp = target - (target == 0);
   return (arma::accu(arma::max(1-input % temp, 0.))) / target.n_elem;
diff --git a/src/mlpack/methods/ann/loss_functions/huber_loss.hpp b/src/mlpack/methods/ann/loss_functions/huber_loss.hpp
index 9a18cfea1b..60e8d96b10 100644
--- a/src/mlpack/methods/ann/loss_functions/huber_loss.hpp
+++ b/src/mlpack/methods/ann/loss_functions/huber_loss.hpp
@@ -52,7 +52,8 @@ class HuberLoss
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/huber_loss_impl.hpp b/src/mlpack/methods/ann/loss_functions/huber_loss_impl.hpp
index 25da492bcf..c9c5ee9145 100644
--- a/src/mlpack/methods/ann/loss_functions/huber_loss_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/huber_loss_impl.hpp
@@ -30,13 +30,15 @@ HuberLoss<InputDataType, OutputDataType>::HuberLoss(
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double HuberLoss<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+HuberLoss<InputDataType, OutputDataType>::Forward(const InputType& input,
+                                                  const TargetType& target)
 {
-  double loss = 0;
+  typedef typename InputType::elem_type ElemType;
+  ElemType loss = 0;
   for (size_t i = 0; i < input.n_elem; ++i)
   {
-      const double absError = std::abs(target[i] - input[i]);
+      const ElemType absError = std::abs(target[i] - input[i]);
       loss += absError > delta
           ? delta * (absError - 0.5 * delta) : 0.5 * std::pow(absError, 2);
   }
@@ -50,13 +52,16 @@ void HuberLoss<InputDataType, OutputDataType>::Backward(
     const TargetType& target,
     OutputType& output)
 {
+  typedef typename InputType::elem_type ElemType;
+
   output.set_size(size(input));
   for (size_t i = 0; i < output.n_elem; ++i)
   {
-    const double absError = std::abs(target[i] - input[i]);
+    const ElemType absError = std::abs(target[i] - input[i]);
     output[i] = absError > delta
         ? - delta * (target[i] - input[i]) / absError : input[i] - target[i];
-    if (mean) output[i] /= output.n_elem;
+    if (mean)
+      output[i] /= output.n_elem;
   }
 }
 
diff --git a/src/mlpack/methods/ann/loss_functions/kl_divergence.hpp b/src/mlpack/methods/ann/loss_functions/kl_divergence.hpp
index ad39d16c62..4640dce43e 100644
--- a/src/mlpack/methods/ann/loss_functions/kl_divergence.hpp
+++ b/src/mlpack/methods/ann/loss_functions/kl_divergence.hpp
@@ -60,7 +60,8 @@ class KLDivergence
    * @param target Target data to compare with.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/kl_divergence_impl.hpp b/src/mlpack/methods/ann/loss_functions/kl_divergence_impl.hpp
index dc72dc1645..bc9b44ea09 100644
--- a/src/mlpack/methods/ann/loss_functions/kl_divergence_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/kl_divergence_impl.hpp
@@ -28,8 +28,9 @@ KLDivergence<InputDataType, OutputDataType>::KLDivergence(const bool takeMean) :
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double KLDivergence<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+KLDivergence<InputDataType, OutputDataType>::Forward(const InputType& input,
+                                                     const TargetType& target)
 {
   if (takeMean)
   {
diff --git a/src/mlpack/methods/ann/loss_functions/log_cosh_loss.hpp b/src/mlpack/methods/ann/loss_functions/log_cosh_loss.hpp
index d528157b11..2fc859c5c7 100644
--- a/src/mlpack/methods/ann/loss_functions/log_cosh_loss.hpp
+++ b/src/mlpack/methods/ann/loss_functions/log_cosh_loss.hpp
@@ -20,7 +20,7 @@ namespace ann /** Artificial Neural Network. */ {
 
 /**
  * The Log-Hyperbolic-Cosine loss function is often used to improve
- * variational auto encoder. This function is the log of hyperbolic 
+ * variational auto encoder. This function is the log of hyperbolic
  * cosine of difference between true values and predicted values.
  *
  * @tparam InputDataType Type of the input data (arma::colvec, arma::mat,
@@ -55,7 +55,8 @@ class LogCoshLoss
    * @param target Target data to compare with.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/log_cosh_loss_impl.hpp b/src/mlpack/methods/ann/loss_functions/log_cosh_loss_impl.hpp
index 5de18340e6..1fd13c922f 100644
--- a/src/mlpack/methods/ann/loss_functions/log_cosh_loss_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/log_cosh_loss_impl.hpp
@@ -28,8 +28,9 @@ LogCoshLoss<InputDataType, OutputDataType>::LogCoshLoss(const double a) :
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double LogCoshLoss<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+LogCoshLoss<InputDataType, OutputDataType>::Forward(const InputType& input,
+                                                    const TargetType& target)
 {
   return arma::accu(arma::log(arma::cosh(a * (target - input)))) / a;
 }
diff --git a/src/mlpack/methods/ann/loss_functions/mean_bias_error.hpp b/src/mlpack/methods/ann/loss_functions/mean_bias_error.hpp
index 40418980d3..a238ac50cb 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_bias_error.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_bias_error.hpp
@@ -45,7 +45,8 @@ class MeanBiasError
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/mean_bias_error_impl.hpp b/src/mlpack/methods/ann/loss_functions/mean_bias_error_impl.hpp
index 8488ae487a..9d014585f4 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_bias_error_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_bias_error_impl.hpp
@@ -27,8 +27,9 @@ MeanBiasError<InputDataType, OutputDataType>::MeanBiasError()
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double MeanBiasError<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+MeanBiasError<InputDataType, OutputDataType>::Forward(const InputType& input,
+                                                      const TargetType& target)
 {
   return arma::accu(target - input) / target.n_cols;
 }
diff --git a/src/mlpack/methods/ann/loss_functions/mean_squared_error.hpp b/src/mlpack/methods/ann/loss_functions/mean_squared_error.hpp
index 6dc6642a0d..0315c10b5c 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_squared_error.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_squared_error.hpp
@@ -46,7 +46,8 @@ class MeanSquaredError
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/mean_squared_error_impl.hpp b/src/mlpack/methods/ann/loss_functions/mean_squared_error_impl.hpp
index d7203b2499..81cf2281cf 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_squared_error_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_squared_error_impl.hpp
@@ -26,8 +26,10 @@ MeanSquaredError<InputDataType, OutputDataType>::MeanSquaredError()
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double MeanSquaredError<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+MeanSquaredError<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   return arma::accu(arma::square(input - target)) / target.n_cols;
 }
diff --git a/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error.hpp b/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error.hpp
index 54b74d17d5..49b94d1d4f 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error.hpp
@@ -45,7 +45,8 @@ class MeanSquaredLogarithmicError
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error_impl.hpp b/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error_impl.hpp
index 4a2aa75d8a..92ead103a7 100644
--- a/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/mean_squared_logarithmic_error_impl.hpp
@@ -27,8 +27,10 @@ MeanSquaredLogarithmicError<InputDataType, OutputDataType>
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double MeanSquaredLogarithmicError<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+MeanSquaredLogarithmicError<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
   return arma::accu(arma::square(arma::log(1. + target) -
       arma::log(1. + input))) / target.n_cols;
diff --git a/src/mlpack/methods/ann/loss_functions/negative_log_likelihood.hpp b/src/mlpack/methods/ann/loss_functions/negative_log_likelihood.hpp
index 200fa1c5f3..6c28321cb9 100644
--- a/src/mlpack/methods/ann/loss_functions/negative_log_likelihood.hpp
+++ b/src/mlpack/methods/ann/loss_functions/negative_log_likelihood.hpp
@@ -48,7 +48,8 @@ class NegativeLogLikelihood
    *        between 1 and the number of classes.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network. The negative log
diff --git a/src/mlpack/methods/ann/loss_functions/negative_log_likelihood_impl.hpp b/src/mlpack/methods/ann/loss_functions/negative_log_likelihood_impl.hpp
index d006b17912..1eb47280c5 100644
--- a/src/mlpack/methods/ann/loss_functions/negative_log_likelihood_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/negative_log_likelihood_impl.hpp
@@ -26,10 +26,13 @@ NegativeLogLikelihood<InputDataType, OutputDataType>::NegativeLogLikelihood()
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-double NegativeLogLikelihood<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+typename InputType::elem_type
+NegativeLogLikelihood<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
-  double output = 0;
+  typedef typename InputType::elem_type ElemType;
+  ElemType output = 0;
   for (size_t i = 0; i < input.n_cols; ++i)
   {
     size_t currentTarget = target(i) - 1;
diff --git a/src/mlpack/methods/ann/loss_functions/reconstruction_loss.hpp b/src/mlpack/methods/ann/loss_functions/reconstruction_loss.hpp
index d8c775efc0..7d7c8e7da6 100644
--- a/src/mlpack/methods/ann/loss_functions/reconstruction_loss.hpp
+++ b/src/mlpack/methods/ann/loss_functions/reconstruction_loss.hpp
@@ -49,7 +49,8 @@ class ReconstructionLoss
    * @param target The target matrix.
    */
   template<typename InputType, typename TargetType>
-  double Forward(const InputType& input, const TargetType& target);
+  typename InputType::elem_type Forward(const InputType& input,
+                                        const TargetType& target);
 
   /**
    * Ordinary feed backward pass of a neural network.
diff --git a/src/mlpack/methods/ann/loss_functions/reconstruction_loss_impl.hpp b/src/mlpack/methods/ann/loss_functions/reconstruction_loss_impl.hpp
index 02ea50f4a7..b47d5bfcdb 100644
--- a/src/mlpack/methods/ann/loss_functions/reconstruction_loss_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/reconstruction_loss_impl.hpp
@@ -30,7 +30,8 @@ ReconstructionLoss<
 
 template<typename InputDataType, typename OutputDataType, typename DistType>
 template<typename InputType, typename TargetType>
-double ReconstructionLoss<InputDataType, OutputDataType, DistType>::Forward(
+typename InputType::elem_type
+ReconstructionLoss<InputDataType, OutputDataType, DistType>::Forward(
     const InputType& input, const TargetType& target)
 {
   dist = DistType(input);
diff --git a/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error.hpp b/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error.hpp
index fec584de8c..0d70d2d29d 100644
--- a/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error.hpp
+++ b/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error.hpp
@@ -64,8 +64,8 @@ class SigmoidCrossEntropyError
    * @param target The target vector.
    */
   template<typename InputType, typename TargetType>
-  inline double Forward(const InputType& input,
-                        const TargetType& target);
+  inline typename InputType::elem_type Forward(const InputType& input,
+                                               const TargetType& target);
   /**
    * Ordinary feed backward pass of a neural network.
    *
diff --git a/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error_impl.hpp b/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error_impl.hpp
index 1ab976874a..e5cf69188c 100644
--- a/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error_impl.hpp
+++ b/src/mlpack/methods/ann/loss_functions/sigmoid_cross_entropy_error_impl.hpp
@@ -29,10 +29,13 @@ SigmoidCrossEntropyError<InputDataType, OutputDataType>
 
 template<typename InputDataType, typename OutputDataType>
 template<typename InputType, typename TargetType>
-inline double SigmoidCrossEntropyError<InputDataType, OutputDataType>::Forward(
-    const InputType& input, const TargetType& target)
+inline typename InputType::elem_type
+SigmoidCrossEntropyError<InputDataType, OutputDataType>::Forward(
+    const InputType& input,
+    const TargetType& target)
 {
-  double maximum = 0;
+  typedef typename InputType::elem_type ElemType;
+  ElemType maximum = 0;
   for (size_t i = 0; i < input.n_elem; ++i)
   {
     maximum += std::max(input[i], 0.0) +
diff --git a/src/mlpack/tests/cv_test.cpp b/src/mlpack/tests/cv_test.cpp
index b4182ac1fb..4210065887 100644
--- a/src/mlpack/tests/cv_test.cpp
+++ b/src/mlpack/tests/cv_test.cpp
@@ -17,6 +17,7 @@
 #include <mlpack/core/cv/metrics/mse.hpp>
 #include <mlpack/core/cv/metrics/precision.hpp>
 #include <mlpack/core/cv/metrics/recall.hpp>
+#include <mlpack/core/cv/metrics/r2_score.hpp>
 #include <mlpack/core/cv/simple_cv.hpp>
 #include <mlpack/core/cv/k_fold_cv.hpp>
 #include <mlpack/methods/ann/ffn.hpp>
@@ -164,6 +165,28 @@ BOOST_AUTO_TEST_CASE(MSETest)
   BOOST_REQUIRE_CLOSE(MSE::Evaluate(lr, data, responses), expectedMSE, 1e-5);
 }
 
+/**
+ * Test the R squared metric (R2 Score).
+ */
+BOOST_AUTO_TEST_CASE(R2ScoreTest)
+{
+  // Making two points that define the linear function f(x) = x - 1.
+  arma::mat trainingData("0 1");
+  arma::rowvec trainingResponses("-1 0");
+
+  LinearRegression lr(trainingData, trainingResponses);
+
+  // Making five responses that are the output of regression function f(x)
+  // with some responses having a slight deviation of 0.005.
+  // Mean Responses = (1 + 2 + 3 + 6 + 8)/5 = 4.
+  arma::mat data("2 3 4 7 9");
+  arma::rowvec responses("1 2.005 3 6.005 8.005");
+
+  double expectedR2 = 0.99999779;
+
+  BOOST_REQUIRE_CLOSE(R2Score::Evaluate(lr, data, responses), expectedR2, 1e-5);
+}
+
 /**
  * Test the mean squared error with matrix responses.
  */