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Java example source code file (LastTimeStepVertex.java)

This example Java source code file (LastTimeStepVertex.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

basegraphvertex, illegalargumentexception, indarray, indarrayindex, invalid, lasttimestepvertex, layer, null, override, pair, runtimeexception, string, vertexindices

The LastTimeStepVertex.java Java example source code

 *  * Copyright 2016 Skymind,Inc.
 *  *
 *  *    Licensed under the Apache License, Version 2.0 (the "License");
 *  *    you may not use this file except in compliance with the License.
 *  *    You may obtain a copy of the License at
 *  *
 *  *        http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  *    Unless required by applicable law or agreed to in writing, software
 *  *    distributed under the License is distributed on an "AS IS" BASIS,
 *  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  *    See the License for the specific language governing permissions and
 *  *    limitations under the License.

package org.deeplearning4j.nn.graph.vertex.impl.rnn;

import org.deeplearning4j.berkeley.Pair;
import org.deeplearning4j.nn.api.Layer;
import org.deeplearning4j.nn.gradient.Gradient;
import org.deeplearning4j.nn.graph.ComputationGraph;
import org.deeplearning4j.nn.graph.vertex.BaseGraphVertex;
import org.deeplearning4j.nn.graph.vertex.VertexIndices;
import org.nd4j.linalg.api.ndarray.INDArray;
import org.nd4j.linalg.factory.Nd4j;
import org.nd4j.linalg.indexing.INDArrayIndex;
import org.nd4j.linalg.indexing.NDArrayIndex;

/** LastTimeStepVertex is used in the context of recurrent neural network activations, to go from 3d (time series)
 * activations to 2d activations, by extracting out the last time step of activations for each example.<br>
 * This can be used for example in sequence to sequence architectures, and potentially for sequence classification.
 * <b>NOTE: Because RNNs may have masking arrays (to allow for examples/time series of different lengths in the same
 * minibatch), it is necessary to provide the same of the network input that has the corresponding mask array. If this
 * input does not have a mask array, the last time step of the input will be used for all examples; otherwise, the time
 * step of the last non-zero entry in the mask array (for each example separately) will be used.
 * @author Alex Black
public class LastTimeStepVertex extends BaseGraphVertex {

    private String inputName;
    private int inputIdx;
    /** Shape of the forward pass activations */
    private int[] fwdPassShape;
    /** Indexes of the time steps that were extracted, for each example */
    private int[] fwdPassTimeSteps;

    public LastTimeStepVertex(ComputationGraph graph, String name, int vertexIndex, String inputName) {
        this(graph, name, vertexIndex, null, null, inputName);

    public LastTimeStepVertex(ComputationGraph graph, String name, int vertexIndex, VertexIndices[] inputVertices,
                              VertexIndices[] outputVertices, String inputName ) {
        super(graph, name, vertexIndex, inputVertices, outputVertices);
        this.inputName = inputName;
        this.inputIdx = graph.getConfiguration().getNetworkInputs().indexOf(inputName);
        if(inputIdx == -1) throw new IllegalArgumentException("Invalid input name: \"" + inputName + "\" not found in list "
            + "of network inputs (" + graph.getConfiguration().getNetworkInputs() + ")");

    public boolean hasLayer() {
        return false;

    public boolean isOutputVertex() {
        return false;

    public Layer getLayer() {
        return null;

    public INDArray doForward(boolean training) {
        //First: get the mask arrays for the given input, if any
        INDArray[] inputMaskArrays = graph.getInputMaskArrays();
        INDArray mask = (inputMaskArrays != null ? inputMaskArrays[inputIdx] : null);

        //Then: work out, from the mask array, which time step of activations we want, extract activations
        //Also: record where they came from (so we can do errors later)
        fwdPassShape = inputs[0].shape();

        INDArray out;
        if(mask == null){
            //No mask array -> extract same (last) column for all
            int lastTS = inputs[0].size(2)-1;
            out = inputs[0].get(NDArrayIndex.all(),NDArrayIndex.all(),NDArrayIndex.point(lastTS));
            fwdPassTimeSteps = null;    //Null -> last time step for all examples
        } else {
            int[] outShape = new int[]{inputs[0].size(0),inputs[0].size(1)};
            out = Nd4j.create(outShape);

            //Want the index of the last non-zero entry in the mask array.
            //Check a little here by using mulRowVector([0,1,2,3,...]) and argmax
            int maxTsLength = fwdPassShape[2];
            INDArray row = Nd4j.linspace(0, maxTsLength - 1, maxTsLength);
            INDArray temp = mask.mulRowVector(row);
            INDArray lastElementIdx = Nd4j.argMax(temp,1);
            fwdPassTimeSteps = new int[fwdPassShape[0]];
            for( int i=0; i<fwdPassTimeSteps.length; i++ ){
                fwdPassTimeSteps[i] = (int)lastElementIdx.getDouble(i);

            //Now, get and assign the corresponding subsets of 3d activations:
            for( int i=0; i<fwdPassTimeSteps.length; i++){

        return out;

    public Pair<Gradient, INDArray[]> doBackward(boolean tbptt) {

        //Allocate the appropriate sized array:
        INDArray epsilonsOut = Nd4j.create(fwdPassShape);

        if(fwdPassTimeSteps == null){
            //Last time step for all examples
            epsilonsOut.put(new INDArrayIndex[]{NDArrayIndex.all(),NDArrayIndex.all(),NDArrayIndex.point(fwdPassShape[2]-1)},
        } else {
            //Different time steps were extracted for each example
            for( int i=0; i<fwdPassTimeSteps.length; i++ ){
                epsilonsOut.put(new INDArrayIndex[]{NDArrayIndex.point(i),NDArrayIndex.all(),
                        NDArrayIndex.point(fwdPassTimeSteps[i])}, epsilons[0].getRow(i));
        return new Pair<>(null,new INDArray[]{epsilonsOut});

    public void setBackpropGradientsViewArray(INDArray backpropGradientsViewArray) {
        if(backpropGradientsViewArray != null) throw new RuntimeException("Vertex does not have gradients; gradients view array cannot be set here");

    public String toString(){
        return "LastTimeStepVertex(inputName="+inputName+")";

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