@Override
    public Tensor evaluate(EvaluationContext<NAMETYPE> context) {
        Tensor a = argumentA.evaluate(context);
        Tensor b = argumentB.evaluate(context);
        if (a instanceof IndexedTensor && b instanceof IndexedTensor) {
            return oldEvaluate(a, b);
        }
        var helper = new Helper(a, b, dimension);
        return helper.result;
    }
Concatenation of two tensors along an (indexed) dimension

@author bratseth
vespajlib/src/main/java/com/yahoo/tensor/functions/Concat.java