org.nd4j.linalg.activations.impl.ActivationSoftmax Maven / Gradle / Ivy
package org.nd4j.linalg.activations.impl;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import org.apache.commons.math3.util.Pair;
import org.nd4j.linalg.activations.BaseActivationFunction;
import org.nd4j.linalg.api.ndarray.INDArray;
import org.nd4j.linalg.api.ops.impl.transforms.SoftMax;
import org.nd4j.linalg.factory.Nd4j;
/**
* f_i(x) = exp(x_i - shift) / sum_j exp(x_j - shift)
* where shift = max_i(x_i)
*/
@EqualsAndHashCode
@Getter
public class ActivationSoftmax extends BaseActivationFunction {
@Override
public INDArray getActivation(INDArray in, boolean training) {
Nd4j.getExecutioner().execAndReturn(new SoftMax(in));
return in;
}
@Override
public Pair backprop(INDArray in, INDArray epsilon) {
/*
//libnd4j only returns diagonal elements, fix in libnd4j?
//derivative of softmax(in) shape = minibatchxclasses should give minibatch x classes x classes
int miniBatchSize = in.shape()[0];
int classSize = in.shape()[1];
//if (in.rank() != 2) throw exception?
INDArray z = Nd4j.zeros(miniBatchSize,classSize,classSize);
INDArray i = Nd4j.eye(classSize);
INDArray out = z.dup();
//identity matrix extended to 3d
Nd4j.getExecutioner().execAndReturn(new BroadcastAddOp(z,i,out,new int[] {1,2}));
//D_jS_j = S_i * (delta_ij - S_j)
Nd4j.getExecutioner().execAndReturn(new BroadcastSubOp(out,in,z,new int[] {0,1}));//1-p or -p
Nd4j.getExecutioner().execAndReturn(new BroadcastMulOp(z,in,out,new int[] {0,1}));//p*(1-p) or -pi*pj
gradient = out;
*/
//use loss fn utils and push this for next release
// Nd4j.getExecutioner().execAndReturn(new SoftMax(in).derivative());
// return in;
INDArray out = Nd4j.getExecutioner().execAndReturn(new SoftMax(in));
INDArray x = out.mul(epsilon).sum(1);
INDArray dLdz = out.mul(epsilon.subColumnVector(x));
return new Pair<>(dLdz, null);
}
@Override
public String toString() {
return "softmax";
}
}