CNTK_2_0_RC_1_Release_Notes

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CNTK v.2.0 RC 1 Release Notes

With Release Candidate 1 the Microsoft Cognitive Toolkit enters the final set of enhancements before release of the production version of CNTK 2.0. We expect no breaking changes before the release of the production version, but we are eager to hear your feedback!

Highlights of CNTK 2.0 Release Candidate 1

The release candidate contains all changes and improvements introduced in CNTK 2.0 during beta phase.

Breaking changes

This release contains the following breaking changes:

• New file names of CNTK Shared Libraries. Read more in this Wiki article.
  • This is important for developers and other users who use explicit CNTK Shared Library file names in their solutions.
  • If you are using CNTK NuGet packages for C++ or C# no action is required (beside updating to the latest NuGet package)
• There is a set of breaking changes in Python and C# API. See the correspondent sections below.

CNTK Core: new and improved features

• Improved performance and memory footprint in CSC/CSR sparse matrix operations.
• Caffe-converted pretrained models on image classification including AlexNet, ResNet, VGG and BN-Inception.
• Multiple-axis slicing.
• Improvements in the device selection API (specifying excluded devices, querying device properties, locking device exclusively).
• Limit the number of sweeps for training.

CNTK Python API

New feature

We enabled support for model debugging in Python (similar to gdb/pdb) by wrapping the model with debug_model() Read more here.

Breaking changes

This release contains the following breaking changes in CNTK Python API:

• Automatic conversion to NumPy array via np.asarray(cntk_obj) is being replaced by asarray()/as_sequences() methods on those objects
  • Reasons:
    • np.assarray() always returns NumPy arrays, so no sequences could be supported
    • np.assarray() only supports dense arrays
    • np.assarray() does not allow to throw exceptions from within the array interface
  • Solution:
    • asarray() returns dense or sparse (instance of scipy.csr_matrix) versions of the underlying data
      • supported by Constant, Parameter, NDArrayView, Value, and MinibatchData
    • as_sequences(var) returns a Python list of sequences whose elements are NumPy arrays (according to var's dynamic and static axes)
      • supported by Value and MinibatchData
• forward() and eval() behave more consistent now
  • Before: when the returned result did had sequences all of same length, they would be returned as a single NumPy array.
  • Now: independent of the sequences, the result will always be a list if the output has a sequence axis. This will impact every usage that has the sequence axis in the output variable (e.g. if you just used input_variable() with standard settings and did not get rid of the sequence axes before the final output node).
• MinibatchData.value is deprecated now because of performance issues
  • Replacement: use MinibatchData.data, which returns a Value instance that does not need to be converted before passing it to the Trainer and thus is much faster.
• Deprecated parameters were removed from training_session. The progress printer should be now passed directly to the trainer, not to the training session. To configure different aspects of the training session, please use configuration objects. In the new version CNTK supports:
  • checkpoint configuration
  • cross validation configuration
  • test configuration

CNTK C#/.NET Managed API

New and improved features

• Support of CSC Sparse input.
• More flexible interface types in API to provide more freedom for developers.
• Improved CLS compliance to better support other .NET languages.
• Performance optimizations.
• Multiple bug fixes, including memory safety and concurrent evaluations.

The updated APIs are described in this Wiki page.

Breaking changes

This release contains the following breaking changes in CNTK C# API:

• The following C# APIs have been moved to new classes:
  • CNTKLib.Alias() -> Function.Alias()
  • CNTKLib.AsComposite() -> Function.AsComposite()
  • CNTKLib.Combine() -> Function.Combine()
  • CNTKLib.SetMaxNumCPUThreads() -> Utils.SetMaxNumCPUThreads()
  • CNTKLib.GetMaxNumCPUThreads() -> Utils.GetMaxNumCPUThreads()
• We have the following two groups of API changes due to signature simplification and certain type changes. These changes may require adaptations in dependent applications.

C# API changes due to type change from uint to int

• Class NDShape

public NDShape(int numAxes, int dimension)
public NDShape(int numAxes)
public int Rank { get; }  
public IList<int> Dimensions { get; }
public int TotalSize { get; }
public int this[int key] { get; }  
public NDShape SubShape(int beginAxisId, int endAxisId)    
public NDShape SubShape(int beginAxisId)    
public static NDShape CreateNDShape(IEnumerable<int> dimensions)

• Class DeviceDescriptor

public int Id { get; }
public static DeviceDescriptor GPUDevice(int deviceId)  

• Class NDArrayView

public NDArrayView(NDShape viewShape, float[] dataBuffer, DeviceDescriptor device, bool readOnly = false)
public NDArrayView(NDShape viewShape, double[] dataBuffer, DeviceDescriptor device, bool readOnly = false) 
public NDArrayView(NDShape viewShape, int[] colStarts, int[] rowIndices, float[] nonZeroValues, DeviceDescriptor device, bool readOnly = false)
public NDArrayView(NDShape viewShape, int[] colStarts, int[] rowIndices, double[] nonZeroValues, DeviceDescriptor device, bool readOnly = false)

• Class NDMask

public int MaskedCount { get; }
public void InvalidateSection(IEnumerable<int> sectionOffset, NDShape sectionShape)
public void MarkSequenceBegin(IEnumerable<int> offset)
public void MarkSequenceBegin(IEnumerable<int> offset, NDShape sectionShape) 

• Class Value

public int MaskedCount { get; }
public static Value CreateBatch<T>(int dimension, IEnumerable<int> batch, DeviceDescriptor device, bool readOnly = false)
public static Value CreateSequence<T>(int dimension, IEnumerable<int> sequence, DeviceDescriptor device, bool readOnly = false)
public static Value CreateSequence<T>(int dimension, IEnumerable<int> sequence, bool sequenceStartFlag, DeviceDescriptor device, bool readOnly = false)
public static Value CreateBatchOfSequences<T>(int dimension, IEnumerable<IEnumerable<int>> batchOfSequences, DeviceDescriptor device, bool readOnly = false)
public static Value CreateBatchOfSequences<T>(int dimension, IEnumerable<IEnumerable<int>> batchOfSequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device,  bool readOnly = false)
public static Value Create<T>(int dimension, IEnumerable<IEnumerable<int>> sequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device, bool readOnly = false)

C# API changes due to type change from concrete class type to interface type

• Class Function

public IList<Variable> Arguments { get; } 
public IList<Variable> Outputs { get; }

• Class Variable

public IList<Axis> DynamicAxes { get; }

• Class Value

public static Value CreateBatch<T>(NDShape sampleShape, IEnumerable<T> batch, DeviceDescriptor device, bool readOnly = false)
public static Value CreateSequence<T>(NDShape sampleShape, IEnumerable<T> sequence, DeviceDescriptor device, bool readOnly = false)
public static Value CreateSequence<T>(NDShape sampleShape, IEnumerable<T> sequence, bool sequenceStartFlag, DeviceDescriptor device, bool readOnly = false)
public static Value CreateBatchOfSequences<T>(NDShape sampleShape, IEnumerable<IEnumerable<T>> batchOfSequences, DeviceDescriptor device, bool readOnly = false)
public static Value CreateBatchOfSequences<T>(NDShape sampleShape, IEnumerable<IEnumerable<T>> batchOfSequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device,  bool readOnly = false)
public static Value Create<T>(NDShape sampleShape, IEnumerable<IEnumerable<T>> sequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device, bool readOnly = false)
public static Value Create<T>(NDShape sampleShape, IEnumerable<IEnumerable<int>> sequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device, bool readOnly = false)
public static Value Create(NDShape sampleShape, IEnumerable<NDArrayView> sequences, DeviceDescriptor device, bool readOnly = false)
public static Value Create(NDShape sampleShape, IEnumerable<NDArrayView> sequences, IEnumerable<bool> sequenceStartFlags, DeviceDescriptor device, bool readOnly = false)

CNTK NuGet package

A new set of NuGet Packages is provided with this Release.

IMPORTANT! In Visual Studio Manage Nuget Packages Window change the default option Stable Only to Include Prerelease. Otherwise the packages will not be visible. The Package version should be 2.0.0-rc1.