@Override
    public TensorFunction<NAMETYPE> withArguments(List<TensorFunction<NAMETYPE>> arguments) {
        if (arguments.size() != 1)
            throw new IllegalArgumentException("Expand must have 1 argument, got " + arguments.size());
        return new Expand<>(arguments.get(0), dimension);
    }
The <i>expand</i> tensor function returns a tensor with a new dimension of
size 1 is added, equivalent to "tensor * tensor(dim_name[1])(1)".

@author lesters
vespajlib/src/main/java/com/yahoo/tensor/functions/Expand.java