nd4j-backends/nd4j-api-parent/nd4j-api/src/main/java/org/nd4j/linalg/factory/BaseNDArrayFactory.java
@Override
    public INDArray toFlattened(Collection<INDArray> matrices) {
        int length = 0;
        for (INDArray m : matrices)
            length += m.length();
        INDArray ret = Nd4j.create(1, length);
        int linearIndex = 0;
        for (INDArray d : matrices) {
            ret.put(new INDArrayIndex[] {NDArrayIndex.interval(linearIndex, linearIndex + d.length())}, d);
            linearIndex += d.length();
        }

        return ret;

    }
@Override
    public INDArray toFlattened(Collection<INDArray> matrices) {
        int length = 0;
        for (INDArray m : matrices)
            length += m.length();
        INDArray ret = Nd4j.create(1, length);
        int linearIndex = 0;
        for (INDArray d : matrices) {
            ret.put(new INDArrayIndex[] {NDArrayIndex.interval(linearIndex, linearIndex + d.length())}, d);
            linearIndex += d.length();
        }

        return ret;

    }
Returns a vector with all of the elements in every nd array
equal to the sum of the lengths of the ndarrays

@param matrices the ndarrays to getFloat a flattened representation of
@return the flattened ndarray