tutorials/intermediate_source/tensorboard_tutorial.rst

Visualizing Models, Data, and Training with TensorBoard
====================================================

In the `60 Minute Blitz <https://pytorch.org/tutorials/beginner/deep_learning_60min_blitz.html>`_, 
we show you how to load in data,
feed it through a model we define as a subclass of ``nn.Module``,
train this model on training data, and test it on test data.
To see what's happening, we print out some statistics as the model
is training to get a sense for whether training is progressing.
However, we can do much better than that: PyTorch integrates with
TensorBoard, a tool designed for visualizing the results of neural
network training runs. This tutorial illustrates some of its
functionality, using the
`Fashion-MNIST dataset <https://github.com/zalandoresearch/fashion-mnist>`__
which can be read into PyTorch using `torchvision.datasets`.

In this tutorial, we'll learn how to:

    1. Read in data and with appropriate transforms (nearly identical to the prior tutorial).
    2. Set up TensorBoard.
    3. Write to TensorBoard.
    4. Inspect a model architecture using TensorBoard.
    5. Use TensorBoard to create interactive versions of the visualizations we created in last tutorial, with less code

Specifically, on point #5, we'll see:

    * A couple of ways to inspect our training data
    * How to track our model's performance as it trains
    * How to assess our model's performance once it is trained.

We'll begin with similar boilerplate code as in the `CIFAR-10 tutorial <https://pytorch.org/tutorials/beginner/blitz/cifar10_tutorial.html>`__:

.. code:: python

    # imports
    import matplotlib.pyplot as plt
    import numpy as np

    import torch
    import torchvision
    import torchvision.transforms as transforms

    import torch.nn as nn
    import torch.nn.functional as F
    import torch.optim as optim

    # transforms
    transform = transforms.Compose(
        [transforms.ToTensor(),
        transforms.Normalize((0.5,), (0.5,))])

    # datasets
    trainset = torchvision.datasets.FashionMNIST('./data',
        download=True,
        train=True,
        transform=transform)
    testset = torchvision.datasets.FashionMNIST('./data',
        download=True,
        train=False,
        transform=transform)

    # dataloaders
    trainloader = torch.utils.data.DataLoader(trainset, batch_size=4,
                                            shuffle=True, num_workers=2)


    testloader = torch.utils.data.DataLoader(testset, batch_size=4,
                                            shuffle=False, num_workers=2)

    # constant for classes
    classes = ('T-shirt/top', 'Trouser', 'Pullover', 'Dress', 'Coat',
            'Sandal', 'Shirt', 'Sneaker', 'Bag', 'Ankle Boot')

    # helper function to show an image
    # (used in the `plot_classes_preds` function below)
    def matplotlib_imshow(img, one_channel=False):
        if one_channel:
            img = img.mean(dim=0)
        img = img / 2 + 0.5     # unnormalize
        npimg = img.numpy()
        if one_channel:
            plt.imshow(npimg, cmap="Greys")
        else:
            plt.imshow(np.transpose(npimg, (1, 2, 0)))

We'll define a similar model architecture from that tutorial, making only
minor modifications to account for the fact that the images are now
one channel instead of three and 28x28 instead of 32x32:

.. code:: python

    class Net(nn.Module):
        def __init__(self):
            super(Net, self).__init__()
            self.conv1 = nn.Conv2d(1, 6, 5)
            self.pool = nn.MaxPool2d(2, 2)
            self.conv2 = nn.Conv2d(6, 16, 5)
            self.fc1 = nn.Linear(16 * 4 * 4, 120)
            self.fc2 = nn.Linear(120, 84)
            self.fc3 = nn.Linear(84, 10)

        def forward(self, x):
            x = self.pool(F.relu(self.conv1(x)))
            x = self.pool(F.relu(self.conv2(x)))
            x = x.view(-1, 16 * 4 * 4)
            x = F.relu(self.fc1(x))
            x = F.relu(self.fc2(x))
            x = self.fc3(x)
            return x


    net = Net()

We'll define the same ``optimizer`` and ``criterion`` from before:

.. code:: python

    criterion = nn.CrossEntropyLoss()
    optimizer = optim.SGD(net.parameters(), lr=0.001, momentum=0.9)

1. TensorBoard setup
~~~~~~~~~~~~~~~~~~~~~

Now we'll set up TensorBoard, importing ``tensorboard`` from ``torch.utils`` and defining a
``SummaryWriter``, our key object for writing information to TensorBoard.

.. code:: python

    from torch.utils.tensorboard import SummaryWriter

    # default `log_dir` is "runs" - we'll be more specific here
    writer = SummaryWriter('runs/fashion_mnist_experiment_1')

Note that this line alone creates a ``runs/fashion_mnist_experiment_1``
folder.

2. Writing to TensorBoard
~~~~~~~~~~~~~~~~~~~~~~~~~

Now let's write an image to our TensorBoard - specifically, a grid -
using `make_grid <https://pytorch.org/docs/stable/torchvision/utils.html#torchvision.utils.make_grid>`__.

.. code:: python

    # get some random training images
    dataiter = iter(trainloader)
    images, labels = dataiter.next()

    # create grid of images
    img_grid = torchvision.utils.make_grid(images)

    # show images
    matplotlib_imshow(img_grid, one_channel=True)

    # write to tensorboard
    writer.add_image('four_fashion_mnist_images', img_grid)

Now running

::

    tensorboard --logdir=runs

from the command line and then navigating to `https://localhost:6006 <https://localhost:6006>`_
should show the following.

.. image:: ../../_static/img/tensorboard_first_view.png

Now you know how to use TensorBoard! This example, however, could be
done in a Jupyter Notebook - where TensorBoard really excels is in
creating interactive visualizations. We'll cover one of those next,
and several more by the end of the tutorial.

3. Inspect the model using TensorBoard
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

One of TensorBoard's strengths is its ability to visualize complex model
structures. Let's visualize the model we built.

.. code:: python

    writer.add_graph(net, images)
    writer.close()

Now upon refreshing TensorBoard you should see a "Graphs" tab that
looks like this:

.. image:: ../../_static/img/tensorboard_model_viz.png

Go ahead and double click on "Net" to see it expand, seeing a
detailed view of the individual operations that make up the model.

TensorBoard has a very handy feature for visualizing high dimensional
data such as image data in a lower dimensional space; we'll cover this
next.

4. Adding a "Projector" to TensorBoard
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We can visualize the lower dimensional representation of higher
dimensional data via the `add_embedding <https://pytorch.org/docs/stable/tensorboard.html#torch.utils.tensorboard.writer.SummaryWriter.add_embedding>`__ method

.. code:: python

    # helper function
    def select_n_random(data, labels, n=100):
        '''
        Selects n random datapoints and their corresponding labels from a dataset
        '''
        assert len(data) == len(labels)

        perm = torch.randperm(len(data))
        return data[perm][:n], labels[perm][:n]

    # select random images and their target indices
    images, labels = select_n_random(trainset.data, trainset.targets)

    # get the class labels for each image
    class_labels = [classes[lab] for lab in labels]

    # log embeddings
    features = images.view(-1, 28 * 28)
    writer.add_embedding(features,
                        metadata=class_labels,
                        label_img=images.unsqueeze(1))
    writer.close()

Now in the "Projector" tab of TensorBoard, you can see these 100
images - each of which is 784 dimensional - projected down into three
dimensional space. Furthermore, this is interactive: you can click
and drag to rotate the three dimensional projection. Finally, a couple
of tips to make the visualization easier to see: select "color: label"
on the top left, as well as enabling "night mode", which will make the
images easier to see since their background is white:

.. image:: ../../_static/img/tensorboard_projector.png

Now we've thoroughly inspected our data, let's show how TensorBoard
can make tracking model training and evaluation clearer, starting with
training.

5. Tracking model training with TensorBoard
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the previous example, we simply *printed* the model's running loss
every 2000 iterations. Now, we'll instead log the running loss to
TensorBoard, along with a view into the predictions the model is
making via the ``plot_classes_preds`` function.

.. code:: python

    # helper functions

    def images_to_probs(net, images):
        '''
        Generates predictions and corresponding probabilities from a trained
        network and a list of images
        '''
        output = net(images)
        # convert output probabilities to predicted class
        _, preds_tensor = torch.max(output, 1)
        preds = np.squeeze(preds_tensor.numpy())
        return preds, [F.softmax(el, dim=0)[i].item() for i, el in zip(preds, output)]


    def plot_classes_preds(net, images, labels):
        '''
        Generates matplotlib Figure using a trained network, along with images
        and labels from a batch, that shows the network's top prediction along
        with its probability, alongside the actual label, coloring this
        information based on whether the prediction was correct or not.
        Uses the "images_to_probs" function.
        '''
        preds, probs = images_to_probs(net, images)
        # plot the images in the batch, along with predicted and true labels
        fig = plt.figure(figsize=(12, 48))
        for idx in np.arange(4):
            ax = fig.add_subplot(1, 4, idx+1, xticks=[], yticks=[])
            matplotlib_imshow(images[idx], one_channel=True)
            ax.set_title("{0}, {1:.1f}%\n(label: {2})".format(
                classes[preds[idx]],
                probs[idx] * 100.0,
                classes[labels[idx]]),
                        color=("green" if preds[idx]==labels[idx].item() else "red"))
        return fig

Finally, let's train the model using the same model training code from
the prior tutorial, but writing results to TensorBoard every 1000
batches instead of printing to console; this is done using the
`add_scalar <https://pytorch.org/docs/stable/tensorboard.html#torch.utils.tensorboard.writer.SummaryWriter.add_scalar>`__
function.

In addition, as we train, we'll generate an image showing the model's
predictions vs. the actual results on the four images included in that
batch.

.. code:: python

    running_loss = 0.0
    for epoch in range(1):  # loop over the dataset multiple times

        for i, data in enumerate(trainloader, 0):

            # get the inputs; data is a list of [inputs, labels]
            inputs, labels = data

            # zero the parameter gradients
            optimizer.zero_grad()

            # forward + backward + optimize
            outputs = net(inputs)
            loss = criterion(outputs, labels)
            loss.backward()
            optimizer.step()

            running_loss += loss.item()
            if i % 1000 == 999:    # every 1000 mini-batches...

                # ...log the running loss
                writer.add_scalar('training loss',
                                running_loss / 1000,
                                epoch * len(trainloader) + i)

                # ...log a Matplotlib Figure showing the model's predictions on a
                # random mini-batch
                writer.add_figure('predictions vs. actuals',
                                plot_classes_preds(net, inputs, labels),
                                global_step=epoch * len(trainloader) + i)
                running_loss = 0.0
    print('Finished Training')

You can now look at the scalars tab to see the running loss plotted
over the 15,000 iterations of training:

.. image:: ../../_static/img/tensorboard_scalar_runs.png

In addition, we can look at the predictions the model made on
arbitrary batches throughout learning. See the "Images" tab and scroll
down under the "predictions vs. actuals" visualization to see this;
this shows us that, for example, after just 3000 training iterations,
the model was already able to distinguish between visually distinct
classes such as shirts, sneakers, and coats, though it isn't as
confident as it becomes later on in training:

.. image:: ../../_static/img/tensorboard_images.png

In the prior tutorial, we looked at per-class accuracy once the model
had been trained; here, we'll use TensorBoard to plot precision-recall
curves (good explanation
`here <https://www.scikit-yb.org/en/latest/api/classifier/prcurve.html>`__)
for each class. 

6. Assessing trained models with TensorBoard
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: python

    # 1. gets the probability predictions in a test_size x num_classes Tensor
    # 2. gets the preds in a test_size Tensor
    # takes ~10 seconds to run
    class_probs = []
    class_preds = []
    with torch.no_grad():
        for data in testloader:
            images, labels = data
            output = net(images)
            class_probs_batch = [F.softmax(el, dim=0) for el in output]
            _, class_preds_batch = torch.max(output, 1)

            class_probs.append(class_probs_batch)
            class_preds.append(class_preds_batch)

    test_probs = torch.cat([torch.stack(batch) for batch in class_probs])
    test_preds = torch.cat(class_preds)

    # helper function
    def add_pr_curve_tensorboard(class_index, test_probs, test_preds, global_step=0):
        '''
        Takes in a "class_index" from 0 to 9 and plots the corresponding
        precision-recall curve
        '''
        tensorboard_preds = test_preds == class_index
        tensorboard_probs = test_probs[:, class_index]

        writer.add_pr_curve(classes[class_index],
                            tensorboard_preds,
                            tensorboard_probs,
                            global_step=global_step)
        writer.close()

    # plot all the pr curves
    for i in range(len(classes)):
        add_pr_curve_tensorboard(i, test_probs, test_preds)

You will now see a "PR Curves" tab that contains the precision-recall
curves for each class. Go ahead and poke around; you'll see that on
some classes the model has nearly 100% "area under the curve",
whereas on others this area is lower:

.. image:: ../../_static/img/tensorboard_pr_curves.png

And that's an intro to TensorBoard and PyTorch's integration with it.
Of course, you could do everything TensorBoard does in your Jupyter
Notebook, but with TensorBoard, you gets visuals that are interactive
by default.