How will I get the number of terms in an object in Cadabra 2?

Question

e.g ,

Ex:={1}^R_{\mu \nu};

Here {1}^R_{\mu \nu} is perturbed Ricci Tensor

I have tried things like :

number_of_terms(Ex);

Cadabra 2 is showing syntax error.

Answer 1

First of all, you cannot use Ex (with a capital E) as a name for an expression, because Ex is the name of the Cadabra expression object. Secondly, you cannot add pre-fix superscripts like this; the best you can do there is to use the LaTeXForm property. So you can do

R1{#}::LaTeXForm("{}^{1}R").
ex:= R1_{\mu\nu};

Now what do you wan to do next? This expression clearly only contains one term. Did you want to compute it for a particular metric and then determine the number of non-zero components?

Comments

I am not sure if there is any algorithm called "number_of_terms" in Cadabra2. Is it? It was in CADABRA1 where it was applied using @number_of_terms. Perhaps the question was about how to get the number of terms in an expression that is sum of many terms.

---

Counting number of child elements is done with Python's standard len, so

ex:=A+B+C+D+E;
len(ex);

gives 5.

---

But note that this may not do what you want when you have single terms with indices, as it always counts the number of children, and when there is only a single term there is no \sum node at the top. So you get

ex:= A_{m n p q};
len(ex);

giving 4. I should probably re-instate number_of_terms to make this easier to catch...