The Computational Network Tool Kit (new label: Microsoft Cognitive Toolkit) is available to the public since January 2016 and is continously developed further. This video provides a high-level view of the toolkit. It can be included as a library in your Python or C++ programs, or used as a standalone machine learning tool through its own model describtion language (BrainScript). (1)


First of all the installation needs sophisticated knowledge of windows or linux systems. CNTK can be installed either from Source Code or from Binary. The Binary installation is much easier but there is no option to change the source code from CNTK. Installation from Source requires Visual Studio and some other libraries installed on your machine. More Information can be found at the Wiki-Page of CNTK.

The detailed installation steps for binary installation can be summarized as follows:

  1. Download and prepare the Microsoft Cognitive Toolkit
  2. Prepare to run PowerShell scripts
  3. Run the Powershell installation script
  4. Update your GPU Driver
  5. Verify the setup from Python
  6. Verify the setup for BrainScript

The detailed installtation steps for installation from source code can be summarized as follows:

  1. Setting all required environment variables in batch mode
  2. Install Visual Studio 2015 with Update 3
  3. Install MKL Library
  4. Install MS-MPI
  5. Install Boost Library
  6. Install Protobuf
  7. Install NVIDIA CUDA 8
  8. Install cuDNN
  9. Install CUB
  10. Install Latest GPU card driver
  11. Download Getting CNTK Source code
  12. Building CNTK
  13. Quick test of CNTK build functionality

  14. Trying CNTK with GPU

  15. Trying the CNTK Python API



There is no graphical user interface or something similar. One can use the toolkit via the command-line or using Visual Studio when installed from Source. What do you need to train your first Network?

  • A configuration file (Written in Brainscript language)
  • A Dataset (i.e. a .txt file with your data and labels inside)
  • CNTK installed correctly on your machine

The training can be starting using the following command in windows terminal:

cntk configFile = "PATH TO YOUR CONFIGFILE"


In CNTK it is possible to perform a cross-validation during Training.


When successfully trained a network one can test the network and get the results in the windows terminal.

Write Output

Alternatively one can get the results from a network written into a .txt file. This is the most common way when dealing with images as output.


Below you can find a short code example for a multi-class classification.

Figure 1: Workflow of CNTK. Configuration Files and Data are used in CNTK to create a Model. This Model is then used for writing the output.


Example Network


# Copyright (c) Microsoft. All rights reserved.
# Licensed under the MIT license. See LICENSE file in the project root for full license information.

# 3 class classification with softmax - cntk script -- Network Description Language

# which commands to run 

# required...
modelPath = "Models/MC.dnn"      # where to write the model to
deviceId = -1                    # -1 means CPU; use 0 for your first GPU, 1 for the second etc.
dimension = 2                    # input data dimensions
labelDimension = 3

# training config
Train = [

    # network description

        # sample and label dimensions
        SDim = $dimension$
        LDim = $labelDimension$

        features = Input (SDim)
        labels   = Input (LDim)

        # parameters to learn
        b = Parameter (LDim, 1)
        w = Parameter (LDim, SDim)

        # operations
        z = w * features + b

        ce = CrossEntropyWithSoftmax (labels, z)
        errs = ClassificationError (labels, z)

        # root nodes
        featureNodes    = (features)
        labelNodes      = (labels)
        criterionNodes  = (ce)
        evaluationNodes = (errs)
        outputNodes     = (z)

    # configuration parameters of the SGD procedure
    SGD = [
        epochSize = 0                   # =0 means size of the training set
        minibatchSize = 25
        learningRatesPerSample = 0.04   # gradient contribution from each sample
        maxEpochs = 50

    # configuration of data reading
    reader = [

        readerType = "CNTKTextFormatReader"
        file = "Train-3Classes_cntk_text.txt"
        input = [
            features = [
                dim = $dimension$
                format = "dense"
            labels = [
                dim = $labelDimension$     # there are 3 different labels
                format = "dense"

# test
Test = [
    action = "test"
    reader = [
        input = [
            features = [
                dim = $dimension$
                format = "dense"
            labels = [
                dim = $labelDimension$     # there are 3 different labels
                format = "dense"

# output the results
Output = [
        input = [
            features = [
                dim = $dimension$
                format = "dense"
            labels = [
                dim = $labelDimension$     # there are 3 different labels
                format = "dense"
    outputPath = "MC.txt"        # dump the output to this text file

# dump parameter values
DumpNodeInfo = [
    action = "dumpNode"
    printValues = true

This example show how to setup a network which can cluster datapoints into different classes. The networks achieves 89.8% accuracy after training 50 Epochs. The result is shown in Figure 2.

3 class decision boundaries

Figure 2: Visualization of the result. The network is clustering the data into three parts.(1)


As you can see the Brainscript language is pretty intuitive and understandable. A hashtag in front of a line or word signals CNTK that it is a comment. So the first active line is "command=". In this example all sections are evaluated. Each section is defined by a name and the commands are written in square brackets. It is also possible to declare variables. To use a defined variable you need to enclose it with $ signs. 
More information about this example can be found here:

Key Characteristics of CNTK

  • CNTK uses stochastic gradient descent algorithm to train a model.
  • Data Readers
    • CNTKTextFormatReader - reads the text-based CNTK format, which supports multiple inputs combined in the same file.
    • UCIFastReader (deprecated) - reads the text-based UCI format, which contains labels and features combined in one file.
    • ImageReader - reads images with paths to the images inside a txt file.
    • HTKMLFReader - reads the HTK/MLF format files, often used in speech recognition applications.
    • LMSequenceReader - reads text-based files that contain word sequences, for predicting word sequences. This is often used in language modeling.
    • LUSequenceReader - reads text-based files that contain word sequences and their labels. This is often used for language understanding.
  • CNTK can perform:

For a full function reference visit: (1)


Figure 3 compares processing speed (frames processed per second) of CNTK to that of four other well-known toolkits. The configuration uses a fully connected 4-layer neural network (see benchmark scripts) and an effective mini batch size (8192). All results were obtained on the same hardware with the respective latest software versions as of Dec 3, 2015. (1)



Figure 3: Speed Comparison of CNTK and other Toolkits. CNTK provides best performance, when using multiple GPUs. It also beats all other tools in the advantage of using multiple machines.(2)


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