/// <summary>
/// Scaled multi-heads attention component with skip connectioned feed forward layers
/// </summary>
/// <param name="inputQ">The input Q tensor</param>
/// <param name="keyMask">The mask for softmax</param>
/// <param name="batchSize">Batch size of input data set</param>
/// <param name="graph">The instance of computing graph</param>
/// <returns>Transformered output tensor</returns>
public (IWeightTensor, IWeightTensor) Perform(IWeightTensor inputQ, IWeightTensor keyMask, int batchSize, IComputeGraph graph, bool outputAttenWeights = false)
{
using IComputeGraph g = graph.CreateSubGraph($"{m_name}_MultiHeadAttention");
int seqLenQ = inputQ.Rows / batchSize;
IWeightTensor inputQNorm = layerNormQ.Norm(inputQ, g);
//Input projections
var weightedQKV = g.View(g.Affine(inputQNorm, QKV, QKVb), dims: new long[] { batchSize, seqLenQ, 3, m_multiHeadNum, m_d });
var allQ = g.Select(weightedQKV, 2, 0);
var allK = g.Select(weightedQKV, 2, 1);
var allV = g.Select(weightedQKV, 2, 2);
//Multi-head attentions
IWeightTensor Qs = g.View(g.AsContiguous(g.Transpose(allQ, 1, 2)), dims: new long[] { batchSize *m_multiHeadNum, seqLenQ, m_d });
IWeightTensor Ks = g.View(g.AsContiguous(g.Transpose(g.Transpose(allK, 1, 2), 2, 3)), dims: new long[] { batchSize *m_multiHeadNum, m_d, seqLenQ });
IWeightTensor Vs = g.View(g.AsContiguous(g.Transpose(allV, 1, 2)), dims: new long[] { batchSize *m_multiHeadNum, seqLenQ, m_d });
// Scaled softmax
float scale = 1.0f / (float)(Math.Sqrt(m_d));
var attn = g.MulBatch(Qs, Ks, scale);
attn = g.View(attn, dims: new long[] { batchSize, m_multiHeadNum, seqLenQ, seqLenQ });
if (keyMask != null)
{
attn = g.Add(attn, keyMask, inPlace: true);
}
var attnProbs = g.Softmax(attn, inPlace: true);
IWeightTensor sumAttnWeights = null;
if (outputAttenWeights)
{
//Merge all attention probs over multi-heads
sumAttnWeights = graph.Sum(attnProbs, 1);
sumAttnWeights = graph.Div(sumAttnWeights, (float)m_multiHeadNum);
sumAttnWeights = graph.View(sumAttnWeights, new long[] { batchSize *seqLenQ, seqLenQ });
}
attnProbs = g.View(attnProbs, dims: new long[] { batchSize *m_multiHeadNum, seqLenQ, seqLenQ });
IWeightTensor o = g.View(g.MulBatch(attnProbs, Vs), dims: new long[] { batchSize, m_multiHeadNum, seqLenQ, m_d });
IWeightTensor W = g.View(g.AsContiguous(g.Transpose(o, 1, 2)), dims: new long[] { batchSize *seqLenQ, m_multiHeadNum *m_d });
// Output projection
IWeightTensor finalAttResults = g.Dropout(g.Affine(W, W0, b0), batchSize, m_dropoutRatio, inPlace: true);
IWeightTensor result = graph.Add(finalAttResults, inputQ, inPlace: true);
return(result, sumAttnWeights);
}
/// <summary>
/// Scaled multi-heads attention component with skip connectioned feed forward layers
/// </summary>
/// <param name="inputQ">The input Q tensor</param>
/// <param name="inputK">The input K tensor</param>
/// <param name="inputV">The input V tensor</param>
/// <param name="keyMask">The mask for softmax</param>
/// <param name="batchSize">Batch size of input data set</param>
/// <param name="graph">The instance of computing graph</param>
/// <returns>Transformered output tensor</returns>
public (IWeightTensor, IWeightTensor) Perform(IWeightTensor inputQ, IWeightTensor inputK, IWeightTensor inputV, IWeightTensor keyMask, int batchSize, IComputeGraph graph, bool outputAttenWeights = false, Dictionary <string, IWeightTensor> cachedTensors = null)
{
string keyName = $"{m_name}_MultiHeadAttention";
using IComputeGraph g = graph.CreateSubGraph(keyName);
int seqLenQ = inputQ.Rows / batchSize;
// SeqLenK must be euqal to SeqLenV
int seqLenK = inputK.Rows / batchSize;
int seqLenV = inputV.Rows / batchSize;
IWeightTensor inputQNorm = layerNormQ.Norm(inputQ, g);
//Input projections
IWeightTensor allQ = g.View(g.Affine(inputQNorm, Q, Qb), dims: new long[] { batchSize, seqLenQ, m_multiHeadNum, m_d });
//Multi-head attentions
IWeightTensor Qs = g.View(g.AsContiguous(g.Transpose(allQ, 1, 2)), dims: new long[] { batchSize *m_multiHeadNum, seqLenQ, m_d });
IWeightTensor Ks = null;
IWeightTensor Vs = null;
if (cachedTensors == null) // We don't use any cached tensors
{
IWeightTensor allK = g.View(g.Affine(inputK, K, Kb), dims: new long[] { batchSize, seqLenK, m_multiHeadNum, m_d });
IWeightTensor allV = g.View(g.Affine(inputV, V, Vb), dims: new long[] { batchSize, seqLenV, m_multiHeadNum, m_d });
Ks = g.View(g.AsContiguous(g.Transpose(g.Transpose(allK, 1, 2), 2, 3)), dims: new long[] { batchSize *m_multiHeadNum, m_d, seqLenK });
Vs = g.View(g.AsContiguous(g.Transpose(allV, 1, 2)), dims: new long[] { batchSize *m_multiHeadNum, seqLenV, m_d });
}
else
{
string KsCacheName = keyName + "_" + nameof(Ks);
string VsCacheName = keyName + "_" + nameof(Vs);
if (cachedTensors.ContainsKey(KsCacheName) == false)
{
IWeightTensor allK = g.View(g.Affine(inputK, K, Kb), dims: new long[] { batchSize, seqLenK, m_multiHeadNum, m_d });
Ks = g.View(g.AsContiguous(g.Transpose(g.Transpose(allK, 1, 2), 2, 3)), dims: new long[] { batchSize *m_multiHeadNum, m_d, seqLenK });
cachedTensors.Add(KsCacheName, Ks.CopyWeightsRef(KsCacheName, Ks.NeedGradient));
}
else
{
Ks = cachedTensors[KsCacheName];
}
if (cachedTensors.ContainsKey(VsCacheName) == false)
{
IWeightTensor allV = g.View(g.Affine(inputV, V, Vb), dims: new long[] { batchSize, seqLenV, m_multiHeadNum, m_d });
Vs = g.View(g.AsContiguous(g.Transpose(allV, 1, 2)), dims: new long[] { batchSize *m_multiHeadNum, seqLenV, m_d });
cachedTensors.Add(VsCacheName, Vs.CopyWeightsRef(VsCacheName, Vs.NeedGradient));
}
else
{
Vs = cachedTensors[VsCacheName];
}
}
// Scaled softmax
float scale = 1.0f / (float)(Math.Sqrt(m_d));
var attn = g.MulBatch(Qs, Ks, scale);
attn = g.View(attn, dims: new long[] { batchSize, m_multiHeadNum, seqLenQ, seqLenK });
if (keyMask != null)
{
attn = g.Add(attn, keyMask, inPlace: true);
}
var attnProbs = g.Softmax(attn, inPlace: true);
IWeightTensor sumAttnWeights = null;
if (outputAttenWeights)
{
sumAttnWeights = g.Select(attnProbs, 1, 0);
for (int i = 1; i < m_multiHeadNum; i++)
{
var tmp = g.Select(attnProbs, 1, i);
sumAttnWeights = g.Add(sumAttnWeights, tmp);
}
sumAttnWeights = graph.Div(sumAttnWeights, (float)m_multiHeadNum);
sumAttnWeights = graph.View(sumAttnWeights, new long[] { batchSize *seqLenQ, seqLenK });
}
attnProbs = g.View(attnProbs, dims: new long[] { batchSize *m_multiHeadNum, seqLenQ, seqLenK });
IWeightTensor o = g.View(g.MulBatch(attnProbs, Vs), dims: new long[] { batchSize, m_multiHeadNum, seqLenQ, m_d });
IWeightTensor W = g.View(g.AsContiguous(g.Transpose(o, 1, 2)), dims: new long[] { batchSize *seqLenQ, m_multiHeadNum *m_d });
// Output projection
IWeightTensor finalAttResults = g.Dropout(g.Affine(W, W0, b0), batchSize, m_dropoutRatio, inPlace: true);
IWeightTensor result = graph.Add(finalAttResults, inputQ, inPlace: true);
return(result, sumAttnWeights);
}