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Declarative Machine Learning
#-------------------------------------------------------------
#
# Licensed to the Apache Software Foundation (ASF) under one
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# to you under the Apache License, Version 2.0 (the
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#-------------------------------------------------------------
/*
* Low-rank Affine (fully-connected) layer.
*
* This layer has three advantages over the affine layer:
* 1. It has significantly lower memory requirement than affine layer making it ideal for devices such as GPUs.
* 2. It implicitly avoids overfitting by minimizing the number of parameters in the neural network.
* 3. It can exploit sparsity-aware fused operators.
*/
forward = function(matrix[double] X, matrix[double] U, matrix[double] V, matrix[double] b)
return (matrix[double] out) {
/*
* Computes the forward pass for a low-rank affine (fully-connected) layer
* with M neurons. The input data has N examples, each with D
* features.
*
* Inputs:
* - X: Inputs, of shape (N, D).
* - U: LHS factor matrix for weights, of shape (D, R).
* - V: RHS factor matrix for weights, of shape (R, M).
* - b: Biases, of shape (1, M).
*
* Outputs:
* - out: Outputs, of shape (N, M).
*/
out = X %*% U %*% V + b
}
backward = function(matrix[double] dout, matrix[double] X,
matrix[double] U, matrix[double] V, matrix[double] b)
return (matrix[double] dX, matrix[double] dU, matrix[double] dV, matrix[double] db) {
/*
* Computes the backward pass for a low-rank fully-connected (affine) layer
* with M neurons.
*
* Inputs:
* - dout: Gradient wrt `out` from upstream, of shape (N, M).
* - X: Inputs, of shape (N, D).
* - U: LHS factor matrix for weights, of shape (D, R).
* - V: RHS factor matrix for weights, of shape (R, M).
* - b: Biases, of shape (1, M).
*
* Outputs:
* - dX: Gradient wrt `X`, of shape (N, D).
* - dU: Gradient wrt `U`, of shape (D, R).
* - dV: Gradient wrt `V`, of shape (R, M).
* - db: Gradient wrt `b`, of shape (1, M).
*/
dX = dout %*% t(V) %*% t(U)
# If out = Z %*% L, then dL = t(Z) %*% dout
# Substituting Z = X %*% U and L = V, we get
dV = t(U) %*% t(X) %*% dout
dU = t(X) %*% dout %*% t(V)
db = colSums(dout)
}
init = function(int D, int M, int R)
return (matrix[double] U, matrix[double] V, matrix[double] b) {
/*
* Initialize the parameters of this layer.
*
* Note: This is just a convenience function, and parameters
* may be initialized manually if needed.
*
* We use the heuristic by He et al., which limits the magnification
* of inputs/gradients during forward/backward passes by scaling
* unit-Gaussian weights by a factor of sqrt(2/n), under the
* assumption of relu neurons.
* - http://arxiv.org/abs/1502.01852
*
* Inputs:
* - D: Dimensionality of the input features (number of features).
* - M: Number of neurons in this layer.
* - R: Rank of U,V matrices such that R << min(D, M).
*
* Outputs:
* - U: LHS factor matrix for weights, of shape (D, R).
* - V: RHS factor matrix for weights, of shape (R, M).
* - b: Biases, of shape (1, M).
*/
U = rand(rows=D, cols=R, pdf="normal") * sqrt(2.0/D)
V = rand(rows=R, cols=M, pdf="normal") * sqrt(2.0/R)
b = matrix(0, rows=1, cols=M)
}