inline tensor5s gru_impl(const tensor5& input,
const std::size_t n_units,
const bool use_bias,
const bool reset_after,
const bool return_sequences,
const float_vec& weights,
const float_vec& recurrent_weights,
const float_vec& bias,
const std::string& activation,
const std::string& recurrent_activation)
{
const std::size_t n_timesteps = input.shape().width_;
const std::size_t n_features = input.shape().depth_;
// weight matrices
const EigenIndex n = EigenIndex(n_units);
const RowMajorMatrix<Dynamic, Dynamic> W = eigen_row_major_mat_from_values(n_features, n_units * 3, weights);
const RowMajorMatrix<Dynamic, Dynamic> U = eigen_row_major_mat_from_values(n_units, n_units * 3, recurrent_weights);
// kernel bias
RowVector<Dynamic> b_x(n_units * 3);
if (use_bias && bias.size() >= 1 * n_units * 3)
std::copy_n(bias.cbegin(), n_units * 3, b_x.data());
else
b_x.setZero();
// recurrent kernel bias
RowVector<Dynamic> b_h(n_units * 3);
if (use_bias && bias.size() >= 2 * n_units * 3)
std::copy_n(bias.cbegin() + static_cast<float_vec::const_iterator::difference_type>(n_units * 3), n_units * 3, b_h.data());
else
b_h.setZero();
// initialize cell output states h
RowVector<Dynamic> h(1, n_units);
h.setZero();
// write input to eigen matrix of shape (timesteps, n_features)
RowMajorMatrix<Dynamic, Dynamic> x(n_timesteps, n_features);
for (std::size_t a_t = 0; a_t < n_timesteps; ++a_t)
for (std::size_t a_f = 0; a_f < n_features; ++a_f)
x(EigenIndex(a_t), EigenIndex(a_f)) = input.get(0, 0, 0, a_t, a_f);
// kernel applied to inputs (with bias), produces shape (timesteps, n_units * 3)
RowMajorMatrix<Dynamic, Dynamic> Wx = x * W;
Wx.rowwise() += b_x;
// get activation functions
auto act_func = get_activation_func(activation);
auto act_func_recurrent = get_activation_func(recurrent_activation);
// computing GRU output
tensor5s gru_result;
if (return_sequences)
gru_result = { tensor5(shape5(1, 1, 1, n_timesteps, n_units), float_type(0)) };
else
gru_result = { tensor5(shape5(1, 1, 1, 1, n_units), float_type(0)) };
for (EigenIndex k = 0; k < EigenIndex(n_timesteps); ++k)
{
RowVector<Dynamic> r;
RowVector<Dynamic> z;
RowVector<Dynamic> m;
// in the formulae below, the following notations are used:
// A b matrix product
// a o b Hadamard (element-wise) product
// x input vector
// h state vector
// W_{x,a} block of the kernel weight matrix corresponding to "a"
// W_{h,a} block of the recurrent kernel weight matrix corresponding to "a"
// b_{x,a} part of the kernel bias vector corresponding to "a"
// b_{h,a} part of the recurrent kernel bias corresponding to "a"
// z update gate vector
// r reset gate vector
if (reset_after)
{
// recurrent kernel applied to timestep (with bias), produces shape (1, n_units * 3)
RowMajorMatrix<1, Dynamic> Uh = h * U;
Uh += b_h;
// z = sigmoid(W_{x,z} x + b_{i,z} + W_{h,z} h + b_{h,z})
z = (Wx.block(k, 0 * n, 1, n) + Uh.block(0, 0 * n, 1, n)).unaryExpr(act_func_recurrent);
// r = sigmoid(W_{x,r} x + b_{i,r} + W_{h,r} h + b_{h,r})
r = (Wx.block(k, 1 * n, 1, n) + Uh.block(0, 1 * n, 1, n)).unaryExpr(act_func_recurrent);
// m = tanh(W_{x,m} x + b_{i,m} + r * (W_{h,m} h + b_{h,m}))
m = (Wx.block(k, 2 * n, 1, n) + (r.array() * Uh.block(0, 2 * n, 1, n).array()).matrix()).unaryExpr(act_func);
}
else
{
// z = sigmoid(W_{x,z} x + b_{x,z} + W_{h,z} h + b_{h,z})
z = (Wx.block(k, 0 * n, 1, n) + h * U.block(0, 0 * n, n, n) + b_h.block(0, 0 * n, 1, n)).unaryExpr(act_func_recurrent);
// r = sigmoid(W_{x,r} x + b_{x,r} + W_{h,r} h + b_{h,r})
r = (Wx.block(k, 1 * n, 1, n) + h * U.block(0, 1 * n, n, n) + b_h.block(0, 1 * n, 1, n)).unaryExpr(act_func_recurrent);
// m = tanh(W_{x,m} x + b_{x,m} + W_{h,m} (r o h) + b_{h,m}))
m = (Wx.block(k, 2 * n, 1, n) + (r.array() * h.array()).matrix() * U.block(0, 2 * n, n, n) + b_h.block(0, 2 * n, 1, n)).unaryExpr(act_func);
}
// output vector: h' = (1 - z) o m + z o h
h = ((1 - z.array()) * m.array() + z.array() * h.array()).matrix();
if (return_sequences)
for (EigenIndex idx = 0; idx < n; ++idx)
gru_result.front().set(0, 0, 0, std::size_t(k), std::size_t(idx), h(idx));
else if (k == EigenIndex(n_timesteps) - 1)
for (EigenIndex idx = 0; idx < n; ++idx)
gru_result.front().set(0, 0, 0, 0, std::size_t(idx), h(idx));
}
return gru_result;
}
