Thanks for the clarification. We can address that in a different jira.
1) //Memory Management? - That is not required. You can remove setting values to null as it is not a big object and java GC should handle that easily.
2) BigDecimal d = ((BigDecimal) n).add(BigDecimal.ZERO);
Why do you have to add zero? Isn't typecast just enough?
3) AlgebraicBigDecimalSumBase - Can you please rename to AlgebraicBigDecimalMathBase and also correct the javadoc to reflect that, so that we can use this class to add MIN and MAX in a different jira in future.
4) Please make a copy of that code for BigInteger as well.
5) Please update testSUM* testcases in TestBuiltin.java for BigInteger and BigDecimal.