**An agent that performs multi-column addition and subtraction with borrowing and carrying, all the way down to counting. No math functions are used.**

This program supports arithmetic ands subtraction between two multi-digit numbers. It formulates the problem in multiple columns. It does not use any math functions. As currently formulated, it uses a table of all single digit addition facts (for addition and one subtraction strategy) and tables of simple subtraction facts and addition by ten to single digits (for a second subtraction strategy). These facts can be converted to a semantic memory access (in the application of compute-result).

Each primitive operator is relatively simple: without complex proposal conditions, control rules, lots of control flags or complex conditional operator applications. The actual execution trace is sometimes a bit tricky, especially for subtraction.

The project supports the automatic generation of random 3 column addition and subtraction problems which are created in generate-problem. The project will execute N of these (set as the value of ^count in initialize-arithmetic).

The project checks that all answers are computed correctly by using Soar's math functions (computed in elaborations/Verify and finish-problem) if an incorrect answer is computed, it is printed out and Soar halts

The two subtraction strategies differ in what initial facts they assume. One of the subtraction strategies assumes the same knowledge as addition (the sum of two single digit numbers and the resulting carry), but involves remapping that knowledge so that it is appropriate for subtraction. For example it knows that if 7 is subtracted from 6 that the answer is 9 and there must be a borrow from the column to the left.

The second subtraction strategy assumes that the system knows how to subtract any single digit (0-9) from the numbers 0-18, and that it has facts to add ten to any single digit (0-9).

The actual trace of a strategy arises from the available operator applications and impasses that arise. For example, in the second strategy, if a larger number is being subtracted from a smaller number, there is an operator no-change impasse because no fact is available for that situation. This is the standard american approach to subtraction. The key rules for this are in process-column/compute-result.soar

The only differences between the two strategies are the available facts and a single rule in process-column that applies the process-column operator by accessing the facts (process-column*apply*compute-result*subtraction). There are rules that only are used by the second strategy (in the compute-result substate), but there is no explicit control to invoke them and they do not have to be disabled during addition or the other subtraction strategy.

Works with chunking (learn --on).

**Soar capabilities**

- Hierarchical task decomposition
- Chunking
- Doing math with just symbol manipulation

**Download Links**

**External Environment**

- None.

**Default Rules**

- None.

**Associated Publications**

- None.

**Developer**

- John Laird

**Soar Versions**

- Soar 9.2+

**Project Type**

- VisualSoar