private TensorType vectorType(TensorType.Builder builder, String name, TensorType.Dimension.Type type, int size) {
        switch (type) {
            case mapped: builder.mapped(name); break;
            case indexedUnbound: builder.indexed(name); break;
            case indexedBound: builder.indexed(name, size); break;
            default: throw new IllegalArgumentException("Dimension type " + type + " not supported");
        }
        return builder.build();
    }
Create a matrix of vectors (in dimension i) where each vector has the dimension x.
This matrix contains the same vectors as returned by createVectors, in a single list element for convenience.
vespajlib/src/test/java/com/yahoo/tensor/TensorTestCase.java