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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.Tanh;
import org.nd4j.linalg.api.ops.impl.transforms.TanhDerivative;
import org.nd4j.linalg.factory.Nd4j;

/**
 *  f(x) = (exp(x) - exp(-x)) / (exp(x) + exp(-x))
 */
@EqualsAndHashCode
@Getter
public class ActivationTanH extends BaseActivationFunction {

    @Override
    public INDArray getActivation(INDArray in, boolean training) {
        Nd4j.getExecutioner().execAndReturn(new Tanh(in));
        return in;
    }

    @Override
    public Pair backprop(INDArray in, INDArray epsilon) {
        INDArray dLdz = Nd4j.getExecutioner().execAndReturn(new TanhDerivative(in));
        dLdz.muli(epsilon);
        return new Pair<>(dLdz, null);
    }

    @Override
    public String toString() {
        return "tanh";
    }

}