dlib/examples/dnn_mnist_advanced_ex.cpp

// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
/*
    This is an example illustrating the use of the deep learning tools from the
    dlib C++ Library.  I'm assuming you have already read the dnn_mnist_ex.cpp
    example.  So in this example program I'm going to go over a number of more
    advanced parts of the API, including:
        - Training on large datasets that don't fit in memory 
        - Defining large networks
        - Accessing and configuring layers in a network
*/


#include <dlib/dnn.h>
#include <iostream>
#include <dlib/data_io.h>

using namespace std;
using namespace dlib;

// ----------------------------------------------------------------------------------------

// Let's start by showing how you can conveniently define large networks.  The
// most important tool for doing this are C++'s alias templates.  These let us
// define new layer types that are combinations of a bunch of other layers.
// These will form the building blocks for more complex networks.

// So let's begin by defining the building block of a residual network (see
// Figure 2 in Deep Residual Learning for Image Recognition by He, Zhang, Ren,
// and Sun).  You can see a few things in this statement.  The most obvious is
// that we have combined a bunch of layers into the name "base_res".  You can
// also see the use of the tag1 layer.  This layer doesn't do any computation.
// It exists solely so other layers can refer to it.  In this case, the
// add_prev1 layer looks for the tag1 layer and will take the tag1 output and
// add it to the input of the add_prev1 layer.  This combination allows us to
// implement skip and residual style networks.  
template <int stride, typename SUBNET> 
using base_res  = relu<add_prev1<bn_con<con<8,3,3,1,1,relu<bn_con<con<8,3,3,stride,stride,tag1<SUBNET>>>>>>>>;

// Let's also define the same block but with all the batch normalization layers
// replaced with affine transform layers.  We will use this type of construction
// when testing our networks.
template <int stride, typename SUBNET> 
using base_ares = relu<add_prev1<affine<con<8,3,3,1,1,relu<affine<con<8,3,3,stride,stride,tag1<SUBNET>>>>>>>>;

// And of course we can define more alias templates based on previously defined
// alias templates.  The _down versions downsample the inputs by a factor of 2
// while the res and ares layer types don't.
template <typename SUBNET> using res       = base_res<1,SUBNET>;
template <typename SUBNET> using res_down  = base_res<2,SUBNET>;
template <typename SUBNET> using ares      = base_ares<1,SUBNET>;
template <typename SUBNET> using ares_down = base_ares<2,SUBNET>;



// Now that we have these convenient aliases, we can define a residual network
// without a lot of typing.  Note the use of a repeat layer.  This special layer
// type allows us to type repeat<9,res<SUBNET>> instead of
// res<res<res<res<res<res<res<res<res<SUBNET>>>>>>>>>.
const unsigned long number_of_classes = 10;
using net_type = loss_multiclass_log<fc<number_of_classes,
                            avg_pool<11,11,11,11,
                            res<res<res<res_down<
                            repeat<9,res, // repeat this layer 9 times
                            res_down<
                            res<
                            input<matrix<unsigned char>>
                            >>>>>>>>>>;


// And finally, let's define a residual network building block that uses
// parametric ReLU units instead of regular ReLU.
template <typename SUBNET> 
using pres  = prelu<add_prev1<bn_con<con<8,3,3,1,1,prelu<bn_con<con<8,3,3,1,1,tag1<SUBNET>>>>>>>>;

// ----------------------------------------------------------------------------------------

int main(int argc, char** argv) try
{
    if (argc != 2)
    {
        cout << "This example needs the MNIST dataset to run!" << endl;
        cout << "You can get MNIST from http://yann.lecun.com/exdb/mnist/" << endl;
        cout << "Download the 4 files that comprise the dataset, decompress them, and" << endl;
        cout << "put them in a folder.  Then give that folder as input to this program." << endl;
        return 1;
    }

    std::vector<matrix<unsigned char>> training_images;
    std::vector<unsigned long> training_labels;
    std::vector<matrix<unsigned char>> testing_images;
    std::vector<unsigned long> testing_labels;
    load_mnist_dataset(argv[1], training_images, training_labels, testing_images, testing_labels);


    // dlib uses cuDNN under the covers.  One of the features of cuDNN is the
    // option to use slower methods that use less RAM or faster methods that use
    // a lot of RAM.  If you find that you run out of RAM on your graphics card
    // then you can call this function and we will request the slower but more
    // RAM frugal cuDNN algorithms.
    set_dnn_prefer_smallest_algorithms();


    // Create a network as defined above.  This network will produce 10 outputs
    // because that's how we defined net_type.  However, fc layers can have the
    // number of outputs they produce changed at runtime.  
    net_type net;
    // So if you wanted to use the same network but override the number of
    // outputs at runtime you can do so like this:
    net_type net2(num_fc_outputs(15));

    // Now, let's imagine we wanted to replace some of the relu layers with
    // prelu layers.  We might do it like this:
    using net_type2 = loss_multiclass_log<fc<number_of_classes,
                                avg_pool<11,11,11,11,
                                pres<res<res<res_down< // 2 prelu layers here
                                tag4<repeat<9,pres,    // 9 groups, each containing 2 prelu layers  
                                res_down<
                                res<
                                input<matrix<unsigned char>>
                                >>>>>>>>>>>;

    // prelu layers have a floating point parameter.  If you want to set it to
    // something other than its default value you can do so like this:
    net_type2 pnet(prelu_(0.2),  
                   prelu_(0.25),
                   repeat_group(prelu_(0.3),prelu_(0.4)) // Initialize all the prelu instances in the repeat 
                                                         // layer.  repeat_group() is needed to group the 
                                                         // things that are part of repeat's block.
                   );
    // As you can see, a network will greedily assign things given to its
    // constructor to the layers inside itself.  The assignment is done in the
    // order the layers are defined, but it will skip layers where the
    // assignment doesn't make sense.  

    // Now let's print the details of the pnet to the screen and inspect it.
    cout << "The pnet has " << pnet.num_layers << " layers in it." << endl;
    cout << pnet << endl;
    // These print statements will output this (I've truncated it since it's
    // long, but you get the idea):
    /*
        The pnet has 125 layers in it.
        layer<0>      loss_multiclass_log
        layer<1>      fc       (num_outputs=10)
        layer<2>      avg_pool (nr=11, nc=11, stride_y=11, _stride_x=11)
        layer<3>      prelu    (initial_param_value=0.2)
        layer<4>      add_prev
        layer<5>      bn_con
        layer<6>      con      (num_filters=8, nr=3, nc=3, stride_y=1, stride_x=1)
        layer<7>      prelu    (initial_param_value=0.25)
        layer<8>      bn_con
        layer<9>      con      (num_filters=8, nr=3, nc=3, stride_y=1, stride_x=1)
        layer<10>     tag1
        ...
        layer<33>     con      (num_filters=8, nr=3, nc=3, stride_y=2, stride_x=2)
        layer<34>     tag1
        layer<35>     tag4
        layer<36>     prelu    (initial_param_value=0.3)
        layer<37>     add_prev
        layer<38>     bn_con
        ...
        layer<114>    con      (num_filters=8, nr=3, nc=3, stride_y=2, stride_x=2)
        layer<115>    tag1
        layer<116>    relu
        layer<117>    add_prev
        layer<118>    bn_con
        layer<119>    con      (num_filters=8, nr=3, nc=3, stride_y=1, stride_x=1)
        layer<120>    relu
        layer<121>    bn_con
        layer<122>    con      (num_filters=8, nr=3, nc=3, stride_y=1, stride_x=1)
        layer<123>    tag1
        layer<124>    input<matrix>
    */

    // Now that we know the index numbers for each layer, we can access them
    // individually using layer<index>(pnet).  For example, to access the output
    // tensor for the first prelu layer we can say:
    layer<3>(pnet).get_output();
    // Or to print the prelu parameter for layer 7 we can say:
    cout << "prelu param: "<< layer<7>(pnet).layer_details().get_initial_param_value() << endl;

    // We can also access layers by their type.  This next statement finds the
    // first tag1 layer in pnet, and is therefore equivalent to calling
    // layer<10>(pnet):
    layer<tag1>(pnet);
    // The tag layers don't do anything at all and exist simply so you can tag
    // parts of your network and access them by layer<tag>().  You can also
    // index relative to a tag.  So for example, to access the layer immediately
    // after tag4 you can say:
    layer<tag4,1>(pnet); // Equivalent to layer<35+1>(pnet).

    // Or to access the layer 2 layers after tag4:
    layer<tag4,2>(pnet);
    // Tagging is a very useful tool for making complex network structures.  For
    // example, the add_prev1 layer is implemented internally by using a call to
    // layer<tag1>().



    // Ok, that's enough talk about defining and inspecting networks.  Let's
    // talk about training networks!

    // The dnn_trainer will use SGD by default, but you can tell it to use
    // different solvers like adam.  
    dnn_trainer<net_type,adam> trainer(net,adam(0.001));
    trainer.be_verbose();
    trainer.set_synchronization_file("mnist_resnet_sync", std::chrono::seconds(100));
    // While the trainer is running it keeps an eye on the training error.  If
    // it looks like the error hasn't decreased for the last 2000 iterations it
    // will automatically reduce the step size by 0.1.  You can change these
    // default parameters to some other values by calling these functions.  Or
    // disable them entirely by setting the shrink amount to 1.
    trainer.set_iterations_without_progress_threshold(2000);
    trainer.set_step_size_shrink_amount(0.1);


    // Now, what if your training dataset is so big it doesn't fit in RAM?  You
    // make mini-batches yourself, any way you like, and you send them to the
    // trainer by repeatedly calling trainer.train_one_step(). 
    //
    // For example, the loop below stream MNIST data to out trainer.
    std::vector<matrix<unsigned char>> mini_batch_samples;
    std::vector<unsigned long> mini_batch_labels; 
    dlib::rand rnd(time(0));
    // Loop until the trainer's automatic shrinking has shrunk the step size by
    // 1e-3.  For the default shrinks amount of 0.1 this means stop after it
    // shrinks it 3 times.
    while(trainer.get_step_size() >= 1e-3)
    {
        mini_batch_samples.clear();
        mini_batch_labels.clear();

        // make a 128 image mini-batch
        while(mini_batch_samples.size() < 128)
        {
            auto idx = rnd.get_random_32bit_number()%training_images.size();
            mini_batch_samples.push_back(training_images[idx]);
            mini_batch_labels.push_back(training_labels[idx]);
        }

        trainer.train_one_step(mini_batch_samples, mini_batch_labels);
    }

    // When you call train_one_step(), the trainer will do its processing in a
    // separate thread.  This allows the main thread to work on loading data
    // while the trainer is busy executing the mini-batches in parallel.
    // However, this also means we need to wait for any mini-batches that are
    // still executing to stop before we mess with the net object.  Calling
    // get_net() performs the necessary synchronization.
    trainer.get_net();


    net.clean();
    serialize("mnist_res_network.dat") << net;


    // Now we have a trained network.  However, it has batch normalization
    // layers in it.  As is customary, we should replace these with simple
    // affine layers before we use the network.  This can be accomplished by
    // making a network type which is identical to net_type but with the batch
    // normalization layers replaced with affine.  For example:
    using test_net_type = loss_multiclass_log<fc<number_of_classes,
                                avg_pool<11,11,11,11,
                                ares<ares<ares<ares_down<
                                repeat<9,res,
                                ares_down<
                                ares<
                                input<matrix<unsigned char>>
                                >>>>>>>>>>;
    // Then we can simply assign our trained net to our testing net.
    test_net_type tnet = net;
    // Or if you only had a file with your trained network you could deserialize
    // it directly into your testing network.  
    deserialize("mnist_res_network.dat") >> tnet;


    // And finally, we can run the testing network over our data.

    std::vector<unsigned long> predicted_labels = tnet(training_images);
    int num_right = 0;
    int num_wrong = 0;
    for (size_t i = 0; i < training_images.size(); ++i)
    {
        if (predicted_labels[i] == training_labels[i])
            ++num_right;
        else
            ++num_wrong;
        
    }
    cout << "training num_right: " << num_right << endl;
    cout << "training num_wrong: " << num_wrong << endl;
    cout << "training accuracy:  " << num_right/(double)(num_right+num_wrong) << endl;

    predicted_labels = tnet(testing_images);
    num_right = 0;
    num_wrong = 0;
    for (size_t i = 0; i < testing_images.size(); ++i)
    {
        if (predicted_labels[i] == testing_labels[i])
            ++num_right;
        else
            ++num_wrong;
        
    }
    cout << "testing num_right: " << num_right << endl;
    cout << "testing num_wrong: " << num_wrong << endl;
    cout << "testing accuracy:  " << num_right/(double)(num_right+num_wrong) << endl;

}
catch(std::exception& e)
{
    cout << e.what() << endl;
}