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DelayedValueNodeBase::BackpropTo() now also uses a masked operation

This commit is contained in:
Frank Seide 2016-09-05 01:08:58 -07:00
Родитель 484059e055
Коммит 61cf0f76d1
2 изменённых файлов: 56 добавлений и 50 удалений
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101
Source/ComputationNetworkLib/RecurrentNodes.cpp
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@ -27,9 +27,10 @@ DelayedValueNodeBase<ElemType, direction>::DelayedValueNodeBase(DEVICEID_TYPE de
ElemType initialActivationValue, const TensorShape& sampleLayout,
size_t timeStep) :
Base(deviceId, name),
m_initialActivationValueMatrix(make_shared<Matrix<ElemType>>(deviceId)),
m_sourceFrameValidMatrix(make_shared<Matrix<ElemType>>(deviceId)),
m_delayedValue(make_shared<Matrix<ElemType>>(deviceId)),
m_initialActivationValueMatrix(make_shared<Matrix<ElemType>>(deviceId))
m_zeroMatrix(make_shared<Matrix<ElemType>>(deviceId)),
m_delayedValue(make_shared<Matrix<ElemType>>(deviceId))
{
m_initialActivationValue = initialActivationValue;
m_timeStep = 1;
@ -37,6 +38,8 @@ DelayedValueNodeBase<ElemType, direction>::DelayedValueNodeBase(DEVICEID_TYPE de
SetDims(sampleLayout, HasMBLayout() /*false at this point*/);
m_initialActivationValueMatrix->Resize(1, 1);
m_initialActivationValueMatrix->SetValue(m_initialActivationValue);
m_zeroMatrix->Resize(1, 1);
m_zeroMatrix->SetValue((ElemType)0);
m_timeStep = (int)timeStep;
}
@ -49,6 +52,7 @@ template<class ElemType, int direction>
auto node = dynamic_pointer_cast<DelayedValueNodeBase<ElemType, direction /*, SequenceStart_or_End*/>>(nodeP);
node->m_timeStep = m_timeStep;
node->m_initialActivationValue = m_initialActivationValue;
node->m_initialActivationValueMatrix->SetValue(m_initialActivationValue);
node->m_delayedValue->SetValue(*m_delayedValue);
if (m_delayedActivationMBLayout)
(node->m_delayedActivationMBLayout = make_shared<MBLayout>())->CopyFrom(m_delayedActivationMBLayout);
@ -83,7 +87,10 @@ template<class ElemType, int direction>
m_delayedValue->Resize(m_sampleLayout.GetNumElements(), 0); // Note: If we try to access history in first minibatch, we shall crash. It would be a consequence of a missing sentence-begin flag
if (modelVersion >= CNTK_MODEL_VERSION_2)
{
fstream >> m_initialActivationValue;
m_initialActivationValueMatrix->SetValue(m_initialActivationValue);
}
}
template<class ElemType, int direction>
@ -101,9 +108,10 @@ template<class ElemType, int direction>
fstream << m_initialActivationValue;
}
// determine which parallel sequences should be copied; return true if we can do all (where we don't care about gaps)
// determine which parallel sequences have a valid source frame to be copied/propagated
// Remember that we ask about copying from the delayed position to the current position.
// Gaps will be considered as "shall be copied", since that gives us a higher chance of collating all.
// This function also determines whether we can do it all (allValid) or none (!anyValid).
// Gaps will be considered as "valid", since that gives us a higher chance of collating all.
template<class ElemType, int direction>
/*private*/ void DelayedValueNodeBase<ElemType, direction>::DetermineValidMask(const FrameRange& frDelayed, bool& anyValid, bool& allValid)
{
@ -113,7 +121,7 @@ template<class ElemType, int direction>
anyValid = true;
return;
}
// create a vector of 0 and 1 for every parallel sequence
// create a vector of 0 and 1 for every parallel sequence:
// 0 --> source frame invalid: do not copy/propagate
// 1 --> source frame valid (or target is gap): copy/propagate
let S = GetNumParallelSequences();
@ -131,7 +139,18 @@ template<class ElemType, int direction>
anyValid = numValid > 0;
allValid = numValid == S;
if (allValid)
return; // all valid (or gap): just copy all --breakpoint has not been hit; that's not right (gaps!)
sin(1.0); // all valid (or gap): just copy all --breakpoint has not been hit; that's not right (gaps!)
}
// convert the m_sourceFrameValid vector into a (potentially GPU-side) TensorView
template<class ElemType, int direction>
/*private*/ TensorView<ElemType> DelayedValueNodeBase<ElemType, direction>::MakeMaskTensor(size_t rank) const
{
// send to Matrix object (likely living on a GPU)
m_sourceFrameValidMatrix->SetValue(1, m_sourceFrameValid.size(), m_deviceId, const_cast<ElemType*>(m_sourceFrameValid.data()), matrixFlagNormal);
// tensor shape is a 1-frame sequence, one element per parallel sequence.
auto tensorShape = TensorShape(1).AppendInPlace(rank, GetMBLayout()->GetNumParallelSequences());
return TensorView<ElemType>(m_sourceFrameValidMatrix, tensorShape);
}
// This function assumes EndForwardProp() to be called after the iteration loop.
@ -158,15 +177,13 @@ template<class ElemType, int direction>
// compute logical position of delayed value
assert(m_timeStep > 0);
//size_t t = fr.t();
// determine the parallel sequences to mask
bool anyValid, allValid;
DetermineValidMask(frDelayed, anyValid, allValid);
// source tensor --considering truncated BPTT
size_t rank = DetermineElementwiseTensorRank();
TensorView<ElemType> inp;
TensorView<ElemType> src;
int t_delayed = (int)(fr.t() + direction * m_timeStep); // this might end up outside the current window
if (t_delayed < 0) // handle special case of truncated BPTT
{
@ -179,7 +196,7 @@ template<class ElemType, int direction>
auto tensorShape = GetTensorShape(rank);
auto slice = TensorSliceWithMBLayoutFor(tensorShape.GetDims(), FrameRange(m_delayedActivationMBLayout, t_delayed/*<0*/ + T_delayedActivation), m_delayedActivationMBLayout);
tensorShape.NarrowTo(slice);
inp = TensorView<ElemType>(m_delayedValue, tensorShape);
src = TensorView<ElemType>(m_delayedValue, tensorShape);
}
else
LogicError("The delay node tries to access past values that are out of bound, possibly because there is no sentence start marker in the MBLayout.");
@ -187,10 +204,10 @@ template<class ElemType, int direction>
else if (t_delayed >= GetNumTimeSteps()) // truncated BPTT goes left-to-right only
LogicError("The delay node tries to access future values that are out of bound, possibly because there is no sentence end marker in the MBLayout.");
else // regular case
inp = Input(0)->ValueTensorFor(rank, frDelayed);
src = Input(0)->ValueTensorFor(rank, frDelayed);
// target tensor
auto out = ValueTensorFor(rank, fr);
auto tgt = ValueTensorFor(rank, fr);
// init value tensor (a [1] tensor with broadcasting)
TensorView<ElemType> init(m_initialActivationValueMatrix, TensorShape(1));
@ -198,20 +215,15 @@ template<class ElemType, int direction>
// now perform the copy operation
if (allValid) // all frames are valid: copy as one tensor-copy operation
{
out.AssignCopyOf(inp);
tgt.AssignCopyOf(src);
}
else if (!anyValid) // no frame is valid: initialize from init value
{
out.AssignCopyOf(init);
tgt.AssignCopyOf(init);
}
else // some are valid, some are not: use a OpCond to select 'inp' for valid and 'init' for invalid frames
else // some are valid, some are not: use a OpCond to select 'src' for valid and 'init' for invalid frames
{
// treat mask like a 1-frame sequence, one element per parallel sequence
m_sourceFrameValidMatrix->SetValue(1, m_sourceFrameValid.size(), m_deviceId, m_sourceFrameValid.data(), matrixFlagNormal);
auto tensorShape = TensorShape(1).AppendInPlace(rank, GetMBLayout()->GetNumParallelSequences());
TensorView<ElemType> cond(m_sourceFrameValidMatrix, tensorShape);
// now assign either input or init value, based on the mask
out.AssignCondOf(cond, inp, init);
tgt.AssignCondOf(MakeMaskTensor(rank), src, init); // assign either input or init value, based on the mask
}
}
@ -256,43 +268,34 @@ template<class ElemType, int direction>
return;
}
// we backpropagated into the delayed frame
FrameRange frDelayed = fr.WithTimeOffset(direction * m_timeStep);
// if delayed input is within valid time range then add its gradient
size_t rank = DetermineElementwiseTensorRank();
size_t t = fr.t();
int t_delayed = (int) (t + direction * m_timeStep); // this might end up outside the current window
if (t_delayed >= 0 && t_delayed < GetNumTimeSteps()) // only propagate if our source is inside the minibatch
{
size_t S = m_pMBLayout->GetNumParallelSequences();
// Boundary frames must not propagate. Gaps must also not propagate.
// if there is a boundary in this frame, we treat each stream separately; otherwise we do all in one go
if (m_pMBLayout->IsGap(fr) || m_pMBLayout->IsBeyondStartOrEnd(frDelayed)) // true if at least one parallel sequence we pull the gradient for has a boundary
// we backpropagated into the delayed frame
FrameRange frTgt = fr.WithTimeStep(t_delayed); // target frame
FrameRange frSrc = frTgt.WithTimeOffset(direction * -m_timeStep); // source frame
// determine the parallel sequences to mask
bool anyValid, allValid;
DetermineValidMask(frSrc, anyValid, allValid);
auto src = GradientTensorFor(rank, frSrc); // incoming gradient from top
auto tgt = Input(0)->GradientTensorFor(rank, frTgt); // outgoing gradient to input
TensorView<ElemType> zero(m_zeroMatrix, TensorShape(1));
if (allValid) // all valid: just jam it over in one go
{
#if 0
m_backpropMask.resize(S);
for (size_t s = 0; s < S; s++)
m_backpropMask[s] = (m_pMBLayout->IsGap(fr.Sequence(s)) || m_pMBLayout->IsBeyondStartOrEnd(frDelayed.Sequence(s))) ? 0 : 1;
m_backpropMaskMatrix.SetValue(m_backpropMask.data()); ...
#endif
for (size_t s = 0; s < S; s++)
tgt.AddCopyOf(src);
}
else if (anyValid) // // some are valid, some are not: use a OpCond tgt select 'src' for valid and 'zero' for invalid frames
{
if (!m_pMBLayout->IsGap(fr.Sequence(s)) && !m_pMBLayout->IsBeyondStartOrEnd(frDelayed.Sequence(s))) // don't propagate boundary frames or gaps
{
auto frm = GradientTensorFor(rank, fr.Sequence(s));
auto to = Input(0)->GradientTensorFor(rank, frDelayed.Sequence(s));
to.AddCopyOf(frm);
}
}
}
else // operate on entire time step in one go (over all parallel sequences)
{
// TODO: change this to a TensorView operation
auto frm = GradientTensorFor(rank, fr);
auto to = Input(0)->GradientTensorFor(rank, frDelayed);
to.AddCopyOf(frm);
tgt.AddCondOf(MakeMaskTensor(rank), src, zero); // now add either source or zero value, based on the mask
}
else // none valid: nothing tgt back-prop
;
}
}

7
Source/ComputationNetworkLib/RecurrentNodes.h
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@ -29,6 +29,7 @@ class DelayedValueNodeBase : public ComputationNode<ElemType>, public IRecurrent
private:
void DetermineValidMask(const FrameRange& frDelayed, bool& anyValid, bool& allValid);
TensorView<ElemType> MakeMaskTensor(size_t rank) const;
protected:
DelayedValueNodeBase(DEVICEID_TYPE deviceId, const wstring& name, ElemType initialActivationValue, const TensorShape& sampleLayout, size_t timeStep);
@ -74,13 +75,15 @@ public:
protected:
ElemType m_initialActivationValue; // starting value for hidden activation vector at boundary
shared_ptr<Matrix<ElemType>> m_initialActivationValueMatrix; // ...and as a potentially GPU-side object
int m_timeStep; // delay in frames (typ. 1)
function<void()> m_attachInputsFn; // for late expansion of inputs (scripting)
vector<ElemType> m_sourceFrameValid; // mask for copying/propagating source frames is prepared here...
shared_ptr<Matrix<ElemType>> m_sourceFrameValidMatrix; // ...and used from here
shared_ptr<Matrix<ElemType>> m_initialActivationValueMatrix; // potentially GPU-side versions
shared_ptr<Matrix<ElemType>> m_sourceFrameValidMatrix;
shared_ptr<Matrix<ElemType>> m_zeroMatrix; // constant [1]-dimensional 0 used for backprop
shared_ptr<Matrix<ElemType>> m_delayedValue; // saves the activation of the previous step that this node points to
MBLayoutPtr m_delayedActivationMBLayout; // layout for m_delayedValue