Func <Variable, Function> CreateModel(int numOutputDimension, int numLstmLayer, int numHiddenDimension)
{
return((input) =>
{
Function model = input;
for (int i = 0; i < numLstmLayer; i++)
{
model = Stabilizer.Build(model, device);
model = LSTM.Build(model, numHiddenDimension, device);
}
model = Dense.Build(model, numOutputDimension, device);
return model;
});
}
/// <summary>
/// This function creates an LSTM block that implements one step of recurrence.
/// It accepts the previous state and outputs its new state as a two-valued tuple (output, cell state)
/// </summary>
/// <typeparam name="TElementType">The data type of the values. May be set to float or double</typeparam>
/// <param name="input">The input to the LSTM</param>
/// <param name="prevOutput">The output of the previous step of the LSTM</param>
/// <param name="prevCellState">The cell state of the previous step of the LSTM</param>
/// <param name="enableSelfStabilization">If True, then all state-related projection will contain a Stabilizer()</param>
/// <param name="device">Device used for the computation of this cell</param>
/// <returns>A function (prev_h, prev_c, input) -> (h, c) that implements one step of a recurrent LSTM layer</returns>
public static Tuple <Function, Function> LSTMCell <TElementType>(Variable input, Variable prevOutput,
Variable prevCellState, bool enableSelfStabilization, DeviceDescriptor device)
{
// TODO: Implements Peephole
int lstmOutputDimension = prevOutput.Shape[0];
int lstmCellDimension = prevCellState.Shape[0];
bool isFloatType = typeof(TElementType) == typeof(float);
DataType dataType = isFloatType ? DataType.Float : DataType.Double;
if (enableSelfStabilization)
{
prevOutput = Stabilizer.Build(prevOutput, device, "StabilizedPrevOutput");
prevCellState = Stabilizer.Build(prevCellState, device, "StabilizedPrevCellState");
}
uint seed = 1;
Parameter W = new Parameter((NDShape) new[] { lstmCellDimension * 4, NDShape.InferredDimension }, dataType,
CNTKLib.GlorotUniformInitializer(1.0, 1, 0, seed++), device, "W");
Parameter b = new Parameter((NDShape) new[] { lstmCellDimension * 4 }, dataType, CNTKLib.GlorotUniformInitializer(1.0, 1, 0, seed++), device, "b");
Variable linearCombination = CNTKLib.Times(W, input, "linearCombinationInput");
Variable linearCombinationPlusBias = CNTKLib.Plus(b, linearCombination, "linearCombinationInputPlusBias");
Parameter H = new Parameter((NDShape) new[] { lstmCellDimension * 4, lstmOutputDimension }, dataType, CNTKLib.GlorotUniformInitializer(1.0, 1, 0, seed++));
Variable linearCombinationPrevOutput = CNTKLib.Times(H, prevOutput, "linearCombinationPreviousOutput");
Variable gateInput = CNTKLib.Plus(linearCombinationPlusBias, linearCombinationPrevOutput, "gateInput");
Variable forgetProjection =
CNTKLib.Slice(gateInput, new AxisVector()
{
new Axis(0)
}, new IntVector()
{
lstmCellDimension * 0
}, new IntVector()
{
lstmCellDimension * 1
});
Variable inputProjection =
CNTKLib.Slice(gateInput, new AxisVector()
{
new Axis(0)
}, new IntVector()
{
lstmCellDimension * 1
}, new IntVector()
{
lstmCellDimension * 2
});
Variable outputProjection =
CNTKLib.Slice(gateInput, new AxisVector()
{
new Axis(0)
}, new IntVector()
{
lstmCellDimension * 2
}, new IntVector()
{
lstmCellDimension * 3
});
Variable candidateProjection =
CNTKLib.Slice(gateInput, new AxisVector()
{
new Axis(0)
}, new IntVector()
{
lstmCellDimension * 3
}, new IntVector()
{
lstmCellDimension * 4
});
Function ft = CNTKLib.Sigmoid(forgetProjection, "ForgetGate");
Function it = CNTKLib.Sigmoid(inputProjection, "InputGate");
Function ot = CNTKLib.Sigmoid(outputProjection, "OutputGate");
Function ctt = CNTKLib.Tanh(candidateProjection, "Candidate");
Function bft = CNTKLib.ElementTimes(prevCellState, ft);
Function bit = CNTKLib.ElementTimes(it, ctt);
Function ct = CNTKLib.Plus(bft, bit, "CellState");
// According to the TrainingCSharp example in CNTK repository, h (output) should be stabilized,
// however, the Python binding only stabilizes the previous output and previous cell state
Function h = CNTKLib.ElementTimes(ot, CNTKLib.Tanh(ct), "Output");
Function c = ct;
if (lstmOutputDimension != lstmCellDimension)
{
Parameter P = new Parameter((NDShape) new[] { lstmOutputDimension, lstmCellDimension }, dataType, CNTKLib.GlorotUniformInitializer(1.0, 1, 0, seed++));
h = CNTKLib.Times(P, h, "StandarizedOutput");
}
return(new Tuple <Function, Function>(h, c));
}
