@Override
    public String toString(ToStringContext<NAMETYPE> context) {
        return "expand(" + argument.toString(context) + ", " + context.resolveBinding(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