Merge pull request #3157 from asimshankar/java-samples

[samples]: Samples using the Java API.

samples/languages/java/README.md

+# TensorFlow for Java: Examples
+
+Examples using the TensorFlow Java API.

samples/languages/java/docker/Dockerfile

+FROM tensorflow/tensorflow:1.4.0
+WORKDIR /
+RUN apt-get update
+RUN apt-get -y install maven openjdk-8-jdk
+RUN mvn dependency:get -Dartifact=org.tensorflow:tensorflow:1.4.0
+RUN mvn dependency:get -Dartifact=org.tensorflow:proto:1.4.0
+CMD ["/bin/bash", "-l"]

samples/languages/java/docker/README.md

+Dockerfile for building an image suitable for running the Java examples.
+
+Typical usage:
+
+```
+docker build -t java-tensorflow .
+docker run -it --rm -v ${PWD}/..:/examples -w /examples java-tensorflow
+```
+
+That second command will pop you into a shell which has all
+the dependencies required to execute the scripts and Java
+examples.
+
+The script `sanity_test.sh` builds this container and runs a compilation
+check on all the maven projects.

samples/languages/java/docker/sanity_test.sh

+#!/bin/bash
+#
+# Silly sanity test
+DIR="$(cd "$(dirname "$0")" && pwd -P)"
+
+docker build -t java-tensorflow .
+docker run -it --rm -v ${PWD}/..:/examples java-tensorflow bash /examples/docker/test_inside_container.sh

samples/languages/java/docker/test_inside_container.sh

+#!/bin/bash
+
+set -ex
+
+cd /examples/label_image
+mvn compile
+
+cd /examples/object_detection
+mvn compile
+
+cd /examples/training
+mvn compile

samples/languages/java/label_image/.gitignore

+images
+src/main/resources
+target

samples/languages/java/label_image/README.md

+# Image Classification Example
+
+1. Download the model:
+   - If you have [TensorFlow 1.4+ for Python installed](https://www.tensorflow.org/install/),
+     run `python ./download.py`
+   - If not, but you have [docker](https://www.docker.com/get-docker) installed,
+     run `download.sh`.
+
+2. Compile [`LabelImage.java`](src/main/java/LabelImage.java):
+
+   ```
+   mvn compile
+   ```
+
+3. Download some sample images:
+   If you already have some images, great. Otherwise `download_sample_images.sh`
+   gets a few.
+
+3. Classify!
+
+   ```
+   mvn -q exec:java -Dexec.args="<path to image file>"
+   ```

samples/languages/java/label_image/download.py

+"""Create an image classification graph.
+
+Script to download a pre-trained image classifier and tweak it so that
+the model accepts raw bytes of an encoded image.
+
+Doing so involves some model-specific normalization of an image.
+Ideally, this would have been part of the image classifier model,
+but the particular model being used didn't include this normalization,
+so this script does the necessary tweaking.
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+from six.moves import urllib
+import os
+import zipfile
+import tensorflow as tf
+
+URL = 'https://storage.googleapis.com/download.tensorflow.org/models/inception5h.zip'
+LABELS_FILE = 'imagenet_comp_graph_label_strings.txt'
+GRAPH_FILE = 'tensorflow_inception_graph.pb'
+
+GRAPH_INPUT_TENSOR = 'input:0'
+GRAPH_PROBABILITIES_TENSOR = 'output:0'
+
+IMAGE_HEIGHT = 224
+IMAGE_WIDTH = 224
+MEAN = 117
+SCALE = 1
+
+LOCAL_DIR = 'src/main/resources'
+
+
+def download():
+  print('Downloading %s' % URL)
+  zip_filename, _ = urllib.request.urlretrieve(URL)
+  with zipfile.ZipFile(zip_filename) as zip:
+    zip.extract(LABELS_FILE)
+    zip.extract(GRAPH_FILE)
+    os.rename(LABELS_FILE, os.path.join(LOCAL_DIR, 'labels.txt'))
+    os.rename(GRAPH_FILE, os.path.join(LOCAL_DIR, 'graph.pb'))
+
+
+def create_graph_to_decode_and_normalize_image():
+  """See file docstring.
+
+  Returns:
+    input: The placeholder to feed the raw bytes of an encoded image.
+    y: A Tensor (the decoded, normalized image) to be fed to the graph.
+  """
+  image = tf.placeholder(tf.string, shape=(), name='encoded_image_bytes')
+  with tf.name_scope("preprocess"):
+    y = tf.image.decode_image(image, channels=3)
+    y = tf.cast(y, tf.float32)
+    y = tf.expand_dims(y, axis=0)
+    y = tf.image.resize_bilinear(y, (IMAGE_HEIGHT, IMAGE_WIDTH))
+    y = (y - MEAN) / SCALE
+  return (image, y)
+
+
+def patch_graph():
+  """Create graph.pb that applies the model in URL to raw image bytes."""
+  with tf.Graph().as_default() as g:
+    input_image, image_normalized = create_graph_to_decode_and_normalize_image()
+    original_graph_def = tf.GraphDef()
+    with open(os.path.join(LOCAL_DIR, 'graph.pb')) as f:
+      original_graph_def.ParseFromString(f.read())
+    softmax = tf.import_graph_def(
+        original_graph_def,
+        name='inception',
+        input_map={GRAPH_INPUT_TENSOR: image_normalized},
+        return_elements=[GRAPH_PROBABILITIES_TENSOR])
+    # We're constructing a graph that accepts a single image (as opposed to a
+    # batch of images), so might as well make the output be a vector of
+    # probabilities, instead of a batch of vectors with batch size 1.
+    output_probabilities = tf.squeeze(softmax, name='probabilities')
+    # Overwrite the graph.
+    with open(os.path.join(LOCAL_DIR, 'graph.pb'), 'w') as f:
+      f.write(g.as_graph_def().SerializeToString())
+    print('------------------------------------------------------------')
+    print('MODEL GRAPH  : graph.pb')
+    print('LABELS       : labels.txt')
+    print('INPUT TENSOR : %s' % input_image.op.name)
+    print('OUTPUT TENSOR: %s' % output_probabilities.op.name)
+
+
+if __name__ == '__main__':
+  if not os.path.exists(LOCAL_DIR):
+    os.makedirs(LOCAL_DIR)
+  download()
+  patch_graph()

samples/languages/java/label_image/download.sh

+#!/bin/bash
+
+DIR="$(cd "$(dirname "$0")" && pwd -P)"
+docker run -it -v ${DIR}:/x -w /x --rm tensorflow/tensorflow:1.4.0 python download.py

samples/languages/java/label_image/download_sample_images.sh

+#!/bin/bash
+DIR=$(dirname $0)
+mkdir -p ${DIR}/images
+cd ${DIR}/images
+
+# Some random images
+curl -o "porcupine.jpg" -L "https://cdn.pixabay.com/photo/2014/11/06/12/46/porcupines-519145_960_720.jpg"
+curl -o "whale.jpg" -L "https://static.pexels.com/photos/417196/pexels-photo-417196.jpeg"
+curl -o "terrier1u.jpg" -L "https://upload.wikimedia.org/wikipedia/commons/3/34/Australian_Terrier_Melly_%282%29.JPG"
+curl -o "terrier2.jpg" -L "https://cdn.pixabay.com/photo/2014/05/13/07/44/yorkshire-terrier-343198_960_720.jpg"

samples/languages/java/label_image/pom.xml

+<project>
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.myorg</groupId>
+    <artifactId>label-image</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <properties>
+      <exec.mainClass>LabelImage</exec.mainClass>
+      <!-- The sample code requires at least JDK 1.7. -->
+      <!-- The maven compiler plugin defaults to a lower version -->
+      <maven.compiler.source>1.7</maven.compiler.source>
+      <maven.compiler.target>1.7</maven.compiler.target>
+    </properties>
+    <dependencies>
+      <dependency>
+        <groupId>org.tensorflow</groupId>
+        <artifactId>tensorflow</artifactId>
+        <version>1.4.0</version>
+      </dependency>
+      <!-- For ByteStreams.toByteArray: https://google.github.io/guava/releases/23.0/api/docs/com/google/common/io/ByteStreams.html --> 
+      <dependency>
+          <groupId>com.google.guava</groupId>
+          <artifactId>guava</artifactId>
+          <version>23.6-jre</version>
+      </dependency>
+    </dependencies>
+</project>

samples/languages/java/label_image/src/main/java/LabelImage.java

+/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+import com.google.common.io.ByteStreams;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+import org.tensorflow.Graph;
+import org.tensorflow.Session;
+import org.tensorflow.Tensor;
+import org.tensorflow.Tensors;
+
+/**
+ * Simplified version of
+ * https://github.com/tensorflow/tensorflow/blob/r1.4/tensorflow/java/src/main/java/org/tensorflow/examples/LabelImage.java
+ */
+public class LabelImage {
+  public static void main(String[] args) throws Exception {
+    if (args.length < 1) {
+      System.err.println("USAGE: Provide a list of image filenames");
+      System.exit(1);
+    }
+    final List<String> labels = loadLabels();
+    try (Graph graph = new Graph();
+        Session session = new Session(graph)) {
+      graph.importGraphDef(loadGraphDef());
+
+      float[] probabilities = null;
+      for (String filename : args) {
+        byte[] bytes = Files.readAllBytes(Paths.get(filename));
+        try (Tensor<String> input = Tensors.create(bytes);
+            Tensor<Float> output =
+                session
+                    .runner()
+                    .feed("encoded_image_bytes", input)
+                    .fetch("probabilities")
+                    .run()
+                    .get(0)
+                    .expect(Float.class)) {
+          if (probabilities == null) {
+            probabilities = new float[(int) output.shape()[0]];
+          }
+          output.copyTo(probabilities);
+          int label = argmax(probabilities);
+          System.out.printf(
+              "%-30s --> %-15s (%.2f%% likely)\n",
+              filename, labels.get(label), probabilities[label] * 100.0);
+        }
+      }
+    }
+  }
+
+  private static byte[] loadGraphDef() throws IOException {
+    try (InputStream is = LabelImage.class.getClassLoader().getResourceAsStream("graph.pb")) {
+      return ByteStreams.toByteArray(is);
+    }
+  }
+
+  private static ArrayList<String> loadLabels() throws IOException {
+    ArrayList<String> labels = new ArrayList<String>();
+    String line;
+    final InputStream is = LabelImage.class.getClassLoader().getResourceAsStream("labels.txt");
+    try (BufferedReader reader = new BufferedReader(new InputStreamReader(is))) {
+      while ((line = reader.readLine()) != null) {
+        labels.add(line);
+      }
+    }
+    return labels;
+  }
+
+  private static int argmax(float[] probabilities) {
+    int best = 0;
+    for (int i = 1; i < probabilities.length; ++i) {
+      if (probabilities[i] > probabilities[best]) {
+        best = i;
+      }
+    }
+    return best;
+  }
+}

samples/languages/java/object_detection/.gitignore

+images
+labels
+models
+src/main/protobuf
+target

samples/languages/java/object_detection/README.md

+# Object Detection in Java
+
+Example of using pre-trained models of the [TensorFlow Object Detection
+API](https://github.com/tensorflow/models/tree/master/research/object_detection)
+in Java.
+
+## Quickstart
+
+1. Download some metadata files:
+   ```
+   ./download.sh
+   ```
+
+2. Download a model from the [object detection API model
+   zoo](https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md).
+   For example:
+   ```
+   mkdir -p models
+   curl -L \
+    http://download.tensorflow.org/models/object_detection/ssd_inception_v2_coco_2017_11_17.tar.gz \
+   | tar -xz -C models/
+   ```
+
+3. Have some test images handy. For example:
+   ```
+   mkdir -p images
+   curl -L -o images/test.jpg \
+     https://pixnio.com/free-images/people/mother-father-and-children-washing-dog-labrador-retriever-outside-in-the-fresh-air-725x483.jpg
+   ```
+
+4. Compile and run!
+   ```
+   mvn -q compile exec:java \
+     -Dexec.args="models/ssd_inception_v2_coco_2017_11_17/saved_model labels/mscoco_label_map.pbtxt images/test.jpg"
+   ```
+
+## Notes
+
+- This example demonstrates the use of the TensorFlow [SavedModel
+  format](https://www.tensorflow.org/programmers_guide/saved_model). If you have
+  TensorFlow for Python installed, you could explore the model to get the names
+  of the tensors using `saved_model_cli` command. For example:
+  ```
+  saved_model_cli show --dir models/ssd_inception_v2_coco_2017_11_17/saved_model/ --all
+  ```
+
+- The file in `src/main/object_detection/protos/` was generated using:
+
+  ```
+  ./download.sh
+  protoc -Isrc/main/protobuf --java_out=src/main/java src/main/protobuf/string_int_label_map.proto
+  ```
+
+  Where `protoc` was downloaded from
+  https://github.com/google/protobuf/releases/tag/v3.5.1

samples/languages/java/object_detection/download.sh

+#!/bin/bash
+
+set -ex
+
+DIR="$(cd "$(dirname "$0")" && pwd -P)"
+cd "${DIR}"
+
+# The protobuf file needed for mapping labels to human readable names.
+# From:
+# https://github.com/tensorflow/models/blob/f87a58c/research/object_detection/protos/string_int_label_map.proto
+mkdir -p src/main/protobuf
+curl -L -o src/main/protobuf/string_int_label_map.proto "https://raw.githubusercontent.com/tensorflow/models/f87a58cd96d45de73c9a8330a06b2ab56749a7fa/research/object_detection/protos/string_int_label_map.proto"
+
+# Labels from:
+# https://github.com/tensorflow/models/tree/865c14c/research/object_detection/data
+mkdir -p labels
+curl -L -o labels/mscoco_label_map.pbtxt "https://raw.githubusercontent.com/tensorflow/models/865c14c1209cb9ae188b2a1b5f0883c72e050d4c/research/object_detection/data/mscoco_label_map.pbtxt"
+curl -L -o labels/oid_bbox_trainable_label_map.pbtxt "https://raw.githubusercontent.com/tensorflow/models/865c14c1209cb9ae188b2a1b5f0883c72e050d4c/research/object_detection/data/oid_bbox_trainable_label_map.pbtxt"

samples/languages/java/object_detection/pom.xml

+<project>
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.myorg</groupId>
+    <artifactId>detect-objects</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <properties>
+      <exec.mainClass>DetectObjects</exec.mainClass>
+      <!-- The sample code requires at least JDK 1.7. -->
+      <!-- The maven compiler plugin defaults to a lower version -->
+      <maven.compiler.source>1.7</maven.compiler.source>
+      <maven.compiler.target>1.7</maven.compiler.target>
+    </properties>
+    <dependencies>
+      <dependency>
+        <groupId>org.tensorflow</groupId>
+        <artifactId>tensorflow</artifactId>
+        <version>1.4.0</version>
+      </dependency>
+      <dependency>
+        <groupId>org.tensorflow</groupId>
+        <artifactId>proto</artifactId>
+        <version>1.4.0</version>
+      </dependency>
+    </dependencies>
+</project>

samples/languages/java/object_detection/src/main/java/DetectObjects.java

+/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+import static object_detection.protos.StringIntLabelMapOuterClass.StringIntLabelMap;
+import static object_detection.protos.StringIntLabelMapOuterClass.StringIntLabelMapItem;
+
+import com.google.protobuf.TextFormat;
+import java.awt.image.BufferedImage;
+import java.awt.image.DataBufferByte;
+import java.io.File;
+import java.io.IOException;
+import java.io.PrintStream;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.List;
+import java.util.Map;
+import javax.imageio.ImageIO;
+import org.tensorflow.SavedModelBundle;
+import org.tensorflow.Tensor;
+import org.tensorflow.framework.MetaGraphDef;
+import org.tensorflow.framework.SignatureDef;
+import org.tensorflow.framework.TensorInfo;
+import org.tensorflow.types.UInt8;
+
+/**
+ * Java inference for the Object Detection API at:
+ * https://github.com/tensorflow/models/blob/master/research/object_detection/
+ */
+public class DetectObjects {
+  public static void main(String[] args) throws Exception {
+    if (args.length < 3) {
+      printUsage(System.err);
+      System.exit(1);
+    }
+    final String[] labels = loadLabels(args[1]);
+    try (SavedModelBundle model = SavedModelBundle.load(args[0], "serve")) {
+      printSignature(model);
+      for (int arg = 2; arg < args.length; arg++) {
+        final String filename = args[arg];
+        List<Tensor<?>> outputs = null;
+        try (Tensor<UInt8> input = makeImageTensor(filename)) {
+          outputs =
+              model
+                  .session()
+                  .runner()
+                  .feed("image_tensor", input)
+                  .fetch("detection_scores")
+                  .fetch("detection_classes")
+                  .fetch("detection_boxes")
+                  .run();
+        }
+        try (Tensor<Float> scoresT = outputs.get(0).expect(Float.class);
+            Tensor<Float> classesT = outputs.get(1).expect(Float.class);
+            Tensor<Float> boxesT = outputs.get(2).expect(Float.class)) {
+          // All these tensors have:
+          // - 1 as the first dimension
+          // - maxObjects as the second dimension
+          // While boxesT will have 4 as the third dimension (2 sets of (x, y) coordinates).
+          // This can be verified by looking at scoresT.shape() etc.
+          int maxObjects = (int) scoresT.shape()[1];
+          float[] scores = scoresT.copyTo(new float[1][maxObjects])[0];
+          float[] classes = classesT.copyTo(new float[1][maxObjects])[0];
+          float[][] boxes = boxesT.copyTo(new float[1][maxObjects][4])[0];
+          // Print all objects whose score is at least 0.5.
+          System.out.printf("* %s\n", filename);
+          boolean foundSomething = false;
+          for (int i = 0; i < scores.length; ++i) {
+            if (scores[i] < 0.5) {
+              continue;
+            }
+            foundSomething = true;
+            System.out.printf("\tFound %-20s (score: %.4f)\n", labels[(int) classes[i]], scores[i]);
+          }
+          if (!foundSomething) {
+            System.out.println("No objects detected with a high enough score.");
+          }
+        }
+      }
+    }
+  }
+
+  private static void printSignature(SavedModelBundle model) throws Exception {
+    MetaGraphDef m = MetaGraphDef.parseFrom(model.metaGraphDef());
+    SignatureDef sig = m.getSignatureDefOrThrow("serving_default");
+    int numInputs = sig.getInputsCount();
+    int i = 1;
+    System.out.println("MODEL SIGNATURE");
+    System.out.println("Inputs:");
+    for (Map.Entry<String, TensorInfo> entry : sig.getInputsMap().entrySet()) {
+      TensorInfo t = entry.getValue();
+      System.out.printf(
+          "%d of %d: %-20s (Node name in graph: %-20s, type: %s)\n",
+          i++, numInputs, entry.getKey(), t.getName(), t.getDtype());
+    }
+    int numOutputs = sig.getOutputsCount();
+    i = 1;
+    System.out.println("Outputs:");
+    for (Map.Entry<String, TensorInfo> entry : sig.getOutputsMap().entrySet()) {
+      TensorInfo t = entry.getValue();
+      System.out.printf(
+          "%d of %d: %-20s (Node name in graph: %-20s, type: %s)\n",
+          i++, numOutputs, entry.getKey(), t.getName(), t.getDtype());
+    }
+    System.out.println("-----------------------------------------------");
+  }
+
+  private static String[] loadLabels(String filename) throws Exception {
+    String text = new String(Files.readAllBytes(Paths.get(filename)), StandardCharsets.UTF_8);
+    StringIntLabelMap.Builder builder = StringIntLabelMap.newBuilder();
+    TextFormat.merge(text, builder);
+    StringIntLabelMap proto = builder.build();
+    int maxId = 0;
+    for (StringIntLabelMapItem item : proto.getItemList()) {
+      if (item.getId() > maxId) {
+        maxId = item.getId();
+      }
+    }
+    String[] ret = new String[maxId + 1];
+    for (StringIntLabelMapItem item : proto.getItemList()) {
+      ret[item.getId()] = item.getDisplayName();
+    }
+    return ret;
+  }
+
+  private static void bgr2rgb(byte[] data) {
+    for (int i = 0; i < data.length; i += 3) {
+      byte tmp = data[i];
+      data[i] = data[i + 2];
+      data[i + 2] = tmp;
+    }
+  }
+
+  private static Tensor<UInt8> makeImageTensor(String filename) throws IOException {
+    BufferedImage img = ImageIO.read(new File(filename));
+    if (img.getType() != BufferedImage.TYPE_3BYTE_BGR) {
+      throw new IOException(
+          String.format(
+              "Expected 3-byte BGR encoding in BufferedImage, found %d (file: %s). This code could be made more robust",
+              img.getType(), filename));
+    }
+    byte[] data = ((DataBufferByte) img.getData().getDataBuffer()).getData();
+    // ImageIO.read seems to produce BGR-encoded images, but the model expects RGB.
+    bgr2rgb(data);
+    final long BATCH_SIZE = 1;
+    final long CHANNELS = 3;
+    long[] shape = new long[] {BATCH_SIZE, img.getHeight(), img.getWidth(), CHANNELS};
+    return Tensor.create(UInt8.class, shape, ByteBuffer.wrap(data));
+  }
+
+  private static void printUsage(PrintStream s) {
+    s.println("USAGE: <model> <label_map> <image> [<image>] [<image>]");
+    s.println("");
+    s.println("Where");
+    s.println("<model> is the path to the SavedModel directory of the model to use.");
+    s.println("        For example, the saved_model directory in tarballs from ");
+    s.println(
+        "        https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md)");
+    s.println("");
+    s.println(
+        "<label_map> is the path to a file containing information about the labels detected by the model.");
+    s.println("            For example, one of the .pbtxt files from ");
+    s.println(
+        "            https://github.com/tensorflow/models/tree/master/research/object_detection/data");
+    s.println("");
+    s.println("<image> is the path to an image file.");
+    s.println("        Sample images can be found from the COCO, Kitti, or Open Images dataset.");
+    s.println(
+        "        See: https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md");
+  }
+}

samples/languages/java/training/.gitignore

+target
+checkpoint

samples/languages/java/training/README.md

+# Training models in Java
+
+Example of training a model (and saving and restoring checkpoints) using the
+TensorFlow Java API.
+
+## Quickstart
+
+1.  Train for a few steps:
+    ```
+    mvn -q compile exec:java -Dexec.args="model/graph.pb checkpoint"
+    ```
+
+2.  Resume training from previous checkpoint and train some more:
+    ```
+    mvn -q exec:java -Dexec.args="model/graph.pb checkpoint"
+    ```
+
+3. Delete checkpoint:
+   ```
+   rm -rf checkpoint
+   ```
+
+
+## Details
+
+The model in `model/graph.pb` represents a very simple linear model:
+
+```
+y = x * W + b
+```
+
+The `graph.pb` file is generated by executing `create_graph.py` in Python.
+
+The training is orchestrated by `src/main/java/Train.java`, which generates
+training data of the form `y = 3.0 * x + 2.0` and over time, using gradient
+descent, the model should "learn" and the value of `W` should converge to 3.0,
+and `b` to 2.0.