From 305c7a86f65decb5871bf899a9e6da4e97fd98e5 Mon Sep 17 00:00:00 2001
From: Marcus Edel <marcus.edel@fu-berlin.de>
Date: Thu, 3 Oct 2019 21:29:25 +0200
Subject: [PATCH 1/4] Expose the instantiated network.

---
 src/mlpack/methods/ann/ffn.hpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/mlpack/methods/ann/ffn.hpp b/src/mlpack/methods/ann/ffn.hpp
index 9e875a16f2..af9ec3ca80 100644
--- a/src/mlpack/methods/ann/ffn.hpp
+++ b/src/mlpack/methods/ann/ffn.hpp
@@ -257,6 +257,14 @@ class FFN
    */
   void Add(LayerTypes<CustomLayers...> layer) { network.push_back(layer); }
 
+  //! Get the network model.
+  const std::vector<LayerTypes<CustomLayers...> >& Model() const
+  {
+    return network;
+  }
+  //! Modify the network model.
+  std::vector<LayerTypes<CustomLayers...> >& Model() { return network; }
+
   //! Return the number of separable functions (the number of predictor points).
   size_t NumFunctions() const { return numFunctions; }
 
@@ -265,7 +273,7 @@ class FFN
   //! Modify the initial point for the optimization.
   arma::mat& Parameters() { return parameter; }
 
-  //! Get the matrix of responses to the input data points.
+  //! Get the matrix of resposnses to the input data points.
   const arma::mat& Responses() const { return responses; }
   //! Modify the matrix of responses to the input data points.
   arma::mat& Responses() { return responses; }

From 57daceb0f1e476a393001260cbe9744e88510c82 Mon Sep 17 00:00:00 2001
From: Marcus Edel <marcus.edel@fu-berlin.de>
Date: Thu, 3 Oct 2019 21:30:04 +0200
Subject: [PATCH 2/4] Test the Model() ffn method.

---
 src/mlpack/tests/feedforward_network_test.cpp | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/src/mlpack/tests/feedforward_network_test.cpp b/src/mlpack/tests/feedforward_network_test.cpp
index c47d633ace..b84f2a557b 100644
--- a/src/mlpack/tests/feedforward_network_test.cpp
+++ b/src/mlpack/tests/feedforward_network_test.cpp
@@ -575,4 +575,41 @@ BOOST_AUTO_TEST_CASE(FFNTrainReturnObjective)
 
   BOOST_REQUIRE_EQUAL(std::isfinite(objVal), true);
 }
+
+/**
+ * Test that FFN::Model() allows us to access the instantiated network.
+ */
+BOOST_AUTO_TEST_CASE(FFNReturnModel)
+{
+  // Create dummy network.
+  FFN<NegativeLogLikelihood<> > model;
+  Linear<>* linearA = new Linear<>(3, 3);
+  model.Add(linearA);
+  Linear<>* linearB = new Linear<>(3, 4);
+  model.Add(linearB);
+
+  // Initialize network parameter.
+  model.ResetParameters();
+
+  // Set all network parameter to one.
+  model.Parameters().ones();
+
+  // Zero the second layer parameter.
+  linearB->Parameters().zeros();
+
+  // Get the layer parameter from layer A and layer B and store them in
+  // parameterA and parameterB.
+  arma::mat parameterA, parameterB;
+  boost::apply_visitor(ParametersVisitor(std::move(parameterA)),
+      model.Model()[0]);
+  boost::apply_visitor(ParametersVisitor(std::move(parameterB)),
+      model.Model()[1]);
+
+  CheckMatrices(parameterA, arma::ones(3 * 3 + 3, 1));
+  CheckMatrices(parameterB, arma::zeros(3 * 4 + 4, 1));
+
+  CheckMatrices(linearA->Parameters(), arma::ones(3 * 3 + 3, 1));
+  CheckMatrices(linearB->Parameters(), arma::zeros(3 * 4 + 4, 1));
+}
+
 BOOST_AUTO_TEST_SUITE_END();

From dae940f24866d5bab3be3c72cfd9ef85b7cd8806 Mon Sep 17 00:00:00 2001
From: Marcus Edel <marcus.edel@fu-berlin.de>
Date: Fri, 4 Oct 2019 20:32:56 +0200
Subject: [PATCH 3/4] Fix spelling issue.

---
 src/mlpack/methods/ann/ffn.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mlpack/methods/ann/ffn.hpp b/src/mlpack/methods/ann/ffn.hpp
index af9ec3ca80..6f34381b23 100644
--- a/src/mlpack/methods/ann/ffn.hpp
+++ b/src/mlpack/methods/ann/ffn.hpp
@@ -273,7 +273,7 @@ class FFN
   //! Modify the initial point for the optimization.
   arma::mat& Parameters() { return parameter; }
 
-  //! Get the matrix of resposnses to the input data points.
+  //! Get the matrix of responses to the input data points.
   const arma::mat& Responses() const { return responses; }
   //! Modify the matrix of responses to the input data points.
   arma::mat& Responses() { return responses; }

From 113ed59889ab1a238c635c3a87fc35f26b82c691 Mon Sep 17 00:00:00 2001
From: Ryan Curtin <ryan@ratml.org>
Date: Sat, 5 Oct 2019 09:47:29 -0400
Subject: [PATCH 4/4] Update history.

---
 HISTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/HISTORY.md b/HISTORY.md
index ea75bbbf30..6c59d9507d 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,6 @@
 ### mlpack ?.?.?
 ###### ????-??-??
+  * Add Model() to the FFN class to access individual layers (#2043).
 
 ### mlpack 3.2.1
 ###### 2019-10-01